Reiterating JavaScript & Node.js iterators

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Reiterating JavaScript & Node.js iterators Luciano Mammino ( ) @loige loige.link/iter RomaJS - June 16, 2021 1

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import { DynamoDBClient, paginateListTables } from '@aws-sdk/client-dynamodb' const client = new DynamoDBClient({}); for await (const page of paginateListTables({ client }, {})) { // page.TableNames is an array of table names for (const tableName of page.TableNames) { console.log(tableName) } } 1 2 3 4 5 6 7 8 9 10 11 12 13 import { DynamoDBClient, paginateListTables } from '@aws-sdk/client-dynamodb' 1 2 3 4 5 const client = new DynamoDBClient({}); 6 7 for await (const page of paginateListTables({ client }, {})) { 8 // page.TableNames is an array of table names 9 for (const tableName of page.TableNames) { 10 console.log(tableName) 11 } 12 } 13 const client = new DynamoDBClient({}); import { 1 DynamoDBClient, 2 paginateListTables 3 } from '@aws-sdk/client-dynamodb' 4 5 6 7 for await (const page of paginateListTables({ client }, {})) { 8 // page.TableNames is an array of table names 9 for (const tableName of page.TableNames) { 10 console.log(tableName) 11 } 12 } 13 for await (const page of paginateListTables({ client }, {})) { } import { 1 DynamoDBClient, 2 paginateListTables 3 } from '@aws-sdk/client-dynamodb' 4 5 const client = new DynamoDBClient({}); 6 7 8 // page.TableNames is an array of table names 9 for (const tableName of page.TableNames) { 10 console.log(tableName) 11 } 12 13 // page.TableNames is an array of table names for (const tableName of page.TableNames) { console.log(tableName) } import { 1 DynamoDBClient, 2 paginateListTables 3 } from '@aws-sdk/client-dynamodb' 4 5 const client = new DynamoDBClient({}); 6 7 for await (const page of paginateListTables({ client }, {})) { 8 9 10 11 12 } 13 import { DynamoDBClient, paginateListTables } from '@aws-sdk/client-dynamodb' const client = new DynamoDBClient({}); for await (const page of paginateListTables({ client }, {})) { // page.TableNames is an array of table names for (const tableName of page.TableNames) { console.log(tableName) } } 1 2 3 4 5 6 7 8 9 10 11 12 13 @loige for await...of (async iterable) 26

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function createCountdown (start) { let nextVal = start return { next () { if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 function createCountdown (start) { } 1 let nextVal = start 2 return { 3 next () { 4 if (nextVal < 0) { 5 return { done: true } 6 } 7 return { 8 done: false, 9 value: nextVal-- 10 } 11 } 12 } 13 14 let nextVal = start function createCountdown (start) { 1 2 return { 3 next () { 4 if (nextVal < 0) { 5 return { done: true } 6 } 7 return { 8 done: false, 9 value: nextVal-- 10 } 11 } 12 } 13 } 14 return { } function createCountdown (start) { 1 let nextVal = start 2 3 next () { 4 if (nextVal < 0) { 5 return { done: true } 6 } 7 return { 8 done: false, 9 value: nextVal-- 10 } 11 } 12 13 } 14 next () { } function createCountdown (start) { 1 let nextVal = start 2 return { 3 4 if (nextVal < 0) { 5 return { done: true } 6 } 7 return { 8 done: false, 9 value: nextVal-- 10 } 11 12 } 13 } 14 if (nextVal < 0) { return { done: true } } function createCountdown (start) { 1 let nextVal = start 2 return { 3 next () { 4 5 6 7 return { 8 done: false, 9 value: nextVal-- 10 } 11 } 12 } 13 } 14 return { done: false, value: nextVal-- } function createCountdown (start) { 1 let nextVal = start 2 return { 3 next () { 4 if (nextVal < 0) { 5 return { done: true } 6 } 7 8 9 10 11 } 12 } 13 } 14 function createCountdown (start) { let nextVal = start return { next () { if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 @loige Countdown iterator const countdown = createCountdown(3) console.log(countdown.next()) // { done: false, value: 3 } console.log(countdown.next()) // { done: false, value: 2 } console.log(countdown.next()) // { done: false, value: 1 } console.log(countdown.next()) // { done: false, value: 0 } console.log(countdown.next()) // { done: true } 29

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import { setTimeout } from 'timers/promises' function createAsyncCountdown (start, delay = 1000) { let nextVal = start return { async next () { await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 } 14 function createAsyncCountdown (start, delay = 1000) { } import { setTimeout } from 'timers/promises' 1 2 3 let nextVal = start 4 return { 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 14 let nextVal = start import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 4 return { 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 } 14 return { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 13 } 14 async next () { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 12 } 13 } 14 @loige const countdown = createAsyncCountdown(3) console.log(await countdown.next()) // { done: false, value: 3 } console.log(await countdown.next()) // { done: false, value: 2 } console.log(await countdown.next()) // { done: false, value: 1 } console.log(await countdown.next()) // { done: false, value: 0 } console.log(await countdown.next()) // { done: true } 38

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import { setTimeout } from 'timers/promises' function createAsyncCountdown (start, delay = 1000) { let nextVal = start return { async next () { await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 } 14 function createAsyncCountdown (start, delay = 1000) { } import { setTimeout } from 'timers/promises' 1 2 3 let nextVal = start 4 return { 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 14 let nextVal = start import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 4 return { 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 } 14 return { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 13 } 14 async next () { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 12 } 13 } 14 await setTimeout(delay) import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 async next () { 6 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 } 14 @loige const countdown = createAsyncCountdown(3) console.log(await countdown.next()) // { done: false, value: 3 } console.log(await countdown.next()) // { done: false, value: 2 } console.log(await countdown.next()) // { done: false, value: 1 } console.log(await countdown.next()) // { done: false, value: 0 } console.log(await countdown.next()) // { done: true } 38

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import { setTimeout } from 'timers/promises' function createAsyncCountdown (start, delay = 1000) { let nextVal = start return { async next () { await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 } 14 function createAsyncCountdown (start, delay = 1000) { } import { setTimeout } from 'timers/promises' 1 2 3 let nextVal = start 4 return { 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 14 let nextVal = start import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 4 return { 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 } 14 return { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 13 } 14 async next () { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 12 } 13 } 14 await setTimeout(delay) import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 async next () { 6 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 } 14 if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 async next () { 6 await setTimeout(delay) 7 8 9 10 11 } 12 } 13 } 14 @loige const countdown = createAsyncCountdown(3) console.log(await countdown.next()) // { done: false, value: 3 } console.log(await countdown.next()) // { done: false, value: 2 } console.log(await countdown.next()) // { done: false, value: 1 } console.log(await countdown.next()) // { done: false, value: 0 } console.log(await countdown.next()) // { done: true } 38

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import { setTimeout } from 'timers/promises' function createAsyncCountdown (start, delay = 1000) { let nextVal = start return { async next () { await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 } 14 function createAsyncCountdown (start, delay = 1000) { } import { setTimeout } from 'timers/promises' 1 2 3 let nextVal = start 4 return { 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 14 let nextVal = start import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 4 return { 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 } 14 return { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 5 async next () { 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 13 } 14 async next () { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 6 await setTimeout(delay) 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 12 } 13 } 14 await setTimeout(delay) import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 async next () { 6 7 if (nextVal < 0) { 8 return { done: true } 9 } 10 return { done: false, value: nextVal-- } 11 } 12 } 13 } 14 if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 let nextVal = start 4 return { 5 async next () { 6 await setTimeout(delay) 7 8 9 10 11 } 12 } 13 } 14 import { setTimeout } from 'timers/promises' function createAsyncCountdown (start, delay = 1000) { let nextVal = start return { async next () { await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 @loige const countdown = createAsyncCountdown(3) console.log(await countdown.next()) // { done: false, value: 3 } console.log(await countdown.next()) // { done: false, value: 2 } console.log(await countdown.next()) // { done: false, value: 1 } console.log(await countdown.next()) // { done: false, value: 0 } console.log(await countdown.next()) // { done: true } 38

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import { setTimeout } from 'timers/promises' function createAsyncCountdown (start, delay = 1000) { return { [Symbol.asyncIterator]: function () { let nextVal = start return { async next () { await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 function createAsyncCountdown (start, delay = 1000) { } import { setTimeout } from 'timers/promises' 1 2 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 17 } 18 return { import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 } 17 } 18 [Symbol.asyncIterator]: function () { return { done: false, value: nextVal-- } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 13 } 14 } 15 } 16 } 17 } 18 let nextVal = start import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 } 17 } 18 @loige const countdown = createAsyncCountdown(3) for await (const value of countdown) { console.log(value) // 3 ... 2 ... 1 ... 0 } 41

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import { setTimeout } from 'timers/promises' function createAsyncCountdown (start, delay = 1000) { return { [Symbol.asyncIterator]: function () { let nextVal = start return { async next () { await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 function createAsyncCountdown (start, delay = 1000) { } import { setTimeout } from 'timers/promises' 1 2 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 17 } 18 return { import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 } 17 } 18 [Symbol.asyncIterator]: function () { return { done: false, value: nextVal-- } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 13 } 14 } 15 } 16 } 17 } 18 let nextVal = start import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 } 17 } 18 return { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 15 } 16 } 17 } 18 @loige const countdown = createAsyncCountdown(3) for await (const value of countdown) { console.log(value) // 3 ... 2 ... 1 ... 0 } 41

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import { setTimeout } from 'timers/promises' function createAsyncCountdown (start, delay = 1000) { return { [Symbol.asyncIterator]: function () { let nextVal = start return { async next () { await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 function createAsyncCountdown (start, delay = 1000) { } import { setTimeout } from 'timers/promises' 1 2 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 17 } 18 return { import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 } 17 } 18 [Symbol.asyncIterator]: function () { return { done: false, value: nextVal-- } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 13 } 14 } 15 } 16 } 17 } 18 let nextVal = start import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 } 17 } 18 return { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 15 } 16 } 17 } 18 async next () { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 14 } 15 } 16 } 17 } 18 @loige const countdown = createAsyncCountdown(3) for await (const value of countdown) { console.log(value) // 3 ... 2 ... 1 ... 0 } 41

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import { setTimeout } from 'timers/promises' function createAsyncCountdown (start, delay = 1000) { return { [Symbol.asyncIterator]: function () { let nextVal = start return { async next () { await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 function createAsyncCountdown (start, delay = 1000) { } import { setTimeout } from 'timers/promises' 1 2 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 17 } 18 return { import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 } 17 } 18 [Symbol.asyncIterator]: function () { return { done: false, value: nextVal-- } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 13 } 14 } 15 } 16 } 17 } 18 let nextVal = start import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 } 17 } 18 return { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 15 } 16 } 17 } 18 async next () { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 14 } 15 } 16 } 17 } 18 await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 async next () { 8 9 10 11 12 13 } 14 } 15 } 16 } 17 } 18 @loige const countdown = createAsyncCountdown(3) for await (const value of countdown) { console.log(value) // 3 ... 2 ... 1 ... 0 } 41

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import { setTimeout } from 'timers/promises' function createAsyncCountdown (start, delay = 1000) { return { [Symbol.asyncIterator]: function () { let nextVal = start return { async next () { await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 function createAsyncCountdown (start, delay = 1000) { } import { setTimeout } from 'timers/promises' 1 2 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 17 } 18 return { import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 } 17 } 18 [Symbol.asyncIterator]: function () { return { done: false, value: nextVal-- } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 5 let nextVal = start 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 13 } 14 } 15 } 16 } 17 } 18 let nextVal = start import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 6 return { 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 } 15 } 16 } 17 } 18 return { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 7 async next () { 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 } 14 15 } 16 } 17 } 18 async next () { } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 8 await setTimeout(delay) 9 if (nextVal < 0) { 10 return { done: true } 11 } 12 return { done: false, value: nextVal-- } 13 14 } 15 } 16 } 17 } 18 await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } import { setTimeout } from 'timers/promises' 1 2 function createAsyncCountdown (start, delay = 1000) { 3 return { 4 [Symbol.asyncIterator]: function () { 5 let nextVal = start 6 return { 7 async next () { 8 9 10 11 12 13 } 14 } 15 } 16 } 17 } 18 import { setTimeout } from 'timers/promises' function createAsyncCountdown (start, delay = 1000) { return { [Symbol.asyncIterator]: function () { let nextVal = start return { async next () { await setTimeout(delay) if (nextVal < 0) { return { done: true } } return { done: false, value: nextVal-- } } } } } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 @loige const countdown = createAsyncCountdown(3) for await (const value of countdown) { console.log(value) // 3 ... 2 ... 1 ... 0 } 41

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import { createReadStream } from 'fs' const sourceStream = createReadStream('bigdata.csv') let bytes = 0 for await (const chunk of sourceStream) { bytes += chunk.length } console.log(`bigdata.csv: ${bytes} bytes`) 1 2 3 4 5 6 7 8 9 10 import { createReadStream } from 'fs' 1 2 const sourceStream = createReadStream('bigdata.csv') 3 4 let bytes = 0 5 for await (const chunk of sourceStream) { 6 bytes += chunk.length 7 } 8 9 console.log(`bigdata.csv: ${bytes} bytes`) 10 const sourceStream = createReadStream('bigdata.csv') import { createReadStream } from 'fs' 1 2 3 4 let bytes = 0 5 for await (const chunk of sourceStream) { 6 bytes += chunk.length 7 } 8 9 console.log(`bigdata.csv: ${bytes} bytes`) 10 let bytes = 0 import { createReadStream } from 'fs' 1 2 const sourceStream = createReadStream('bigdata.csv') 3 4 5 for await (const chunk of sourceStream) { 6 bytes += chunk.length 7 } 8 9 console.log(`bigdata.csv: ${bytes} bytes`) 10 for await (const chunk of sourceStream) { } import { createReadStream } from 'fs' 1 2 const sourceStream = createReadStream('bigdata.csv') 3 4 let bytes = 0 5 6 bytes += chunk.length 7 8 9 console.log(`bigdata.csv: ${bytes} bytes`) 10 bytes += chunk.length import { createReadStream } from 'fs' 1 2 const sourceStream = createReadStream('bigdata.csv') 3 4 let bytes = 0 5 for await (const chunk of sourceStream) { 6 7 } 8 9 console.log(`bigdata.csv: ${bytes} bytes`) 10 console.log(`bigdata.csv: ${bytes} bytes`) import { createReadStream } from 'fs' 1 2 const sourceStream = createReadStream('bigdata.csv') 3 4 let bytes = 0 5 for await (const chunk of sourceStream) { 6 bytes += chunk.length 7 } 8 9 10 import { createReadStream } from 'fs' const sourceStream = createReadStream('bigdata.csv') let bytes = 0 for await (const chunk of sourceStream) { bytes += chunk.length } console.log(`bigdata.csv: ${bytes} bytes`) 1 2 3 4 5 6 7 8 9 10 @loige Node.js readable streams are async iterators 46

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import { createReadStream } from 'fs' import { once } from 'events' const sourceStream = createReadStream('bigdata.csv') const destStream = new SlowTransform() for await (const chunk of sourceStream) { const canContinue = destStream.write(chunk) if (!canContinue) { // backpressure, now we stop and we need to wait for drain await once(destStream, 'drain') // ok now it's safe to resume writing } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 import { createReadStream } from 'fs' import { once } from 'events' 1 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 const sourceStream = createReadStream('bigdata.csv') import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 const destStream = new SlowTransform() import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 for await (const chunk of sourceStream) { } import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 14 @loige 48

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import { createReadStream } from 'fs' import { once } from 'events' const sourceStream = createReadStream('bigdata.csv') const destStream = new SlowTransform() for await (const chunk of sourceStream) { const canContinue = destStream.write(chunk) if (!canContinue) { // backpressure, now we stop and we need to wait for drain await once(destStream, 'drain') // ok now it's safe to resume writing } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 import { createReadStream } from 'fs' import { once } from 'events' 1 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 const sourceStream = createReadStream('bigdata.csv') import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 const destStream = new SlowTransform() import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 for await (const chunk of sourceStream) { } import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 14 const canContinue = destStream.write(chunk) import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 @loige 48

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import { createReadStream } from 'fs' import { once } from 'events' const sourceStream = createReadStream('bigdata.csv') const destStream = new SlowTransform() for await (const chunk of sourceStream) { const canContinue = destStream.write(chunk) if (!canContinue) { // backpressure, now we stop and we need to wait for drain await once(destStream, 'drain') // ok now it's safe to resume writing } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 import { createReadStream } from 'fs' import { once } from 'events' 1 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 const sourceStream = createReadStream('bigdata.csv') import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 const destStream = new SlowTransform() import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 for await (const chunk of sourceStream) { } import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 14 const canContinue = destStream.write(chunk) import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 if (!canContinue) { } import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 13 } 14 @loige 48

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import { createReadStream } from 'fs' import { once } from 'events' const sourceStream = createReadStream('bigdata.csv') const destStream = new SlowTransform() for await (const chunk of sourceStream) { const canContinue = destStream.write(chunk) if (!canContinue) { // backpressure, now we stop and we need to wait for drain await once(destStream, 'drain') // ok now it's safe to resume writing } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 import { createReadStream } from 'fs' import { once } from 'events' 1 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 const sourceStream = createReadStream('bigdata.csv') import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 const destStream = new SlowTransform() import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 for await (const chunk of sourceStream) { } import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 14 const canContinue = destStream.write(chunk) import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 if (!canContinue) { } import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 13 } 14 // backpressure, now we stop and we need to wait for drain await once(destStream, 'drain') import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 10 11 // ok now it's safe to resume writing 12 } 13 } 14 @loige 48

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import { createReadStream } from 'fs' import { once } from 'events' const sourceStream = createReadStream('bigdata.csv') const destStream = new SlowTransform() for await (const chunk of sourceStream) { const canContinue = destStream.write(chunk) if (!canContinue) { // backpressure, now we stop and we need to wait for drain await once(destStream, 'drain') // ok now it's safe to resume writing } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 import { createReadStream } from 'fs' import { once } from 'events' 1 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 const sourceStream = createReadStream('bigdata.csv') import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 const destStream = new SlowTransform() import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 for await (const chunk of sourceStream) { } import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 14 const canContinue = destStream.write(chunk) import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 if (!canContinue) { } import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 13 } 14 // backpressure, now we stop and we need to wait for drain await once(destStream, 'drain') import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 10 11 // ok now it's safe to resume writing 12 } 13 } 14 // ok now it's safe to resume writing import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 12 } 13 } 14 @loige 48

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import { createReadStream } from 'fs' import { once } from 'events' const sourceStream = createReadStream('bigdata.csv') const destStream = new SlowTransform() for await (const chunk of sourceStream) { const canContinue = destStream.write(chunk) if (!canContinue) { // backpressure, now we stop and we need to wait for drain await once(destStream, 'drain') // ok now it's safe to resume writing } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 import { createReadStream } from 'fs' import { once } from 'events' 1 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 const sourceStream = createReadStream('bigdata.csv') import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 const destStream = new SlowTransform() import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 for await (const chunk of sourceStream) { } import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 14 const canContinue = destStream.write(chunk) import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 } 13 } 14 if (!canContinue) { } import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 // ok now it's safe to resume writing 12 13 } 14 // backpressure, now we stop and we need to wait for drain await once(destStream, 'drain') import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 10 11 // ok now it's safe to resume writing 12 } 13 } 14 // ok now it's safe to resume writing import { createReadStream } from 'fs' 1 import { once } from 'events' 2 3 const sourceStream = createReadStream('bigdata.csv') 4 const destStream = new SlowTransform() 5 6 for await (const chunk of sourceStream) { 7 const canContinue = destStream.write(chunk) 8 if (!canContinue) { 9 // backpressure, now we stop and we need to wait for drain 10 await once(destStream, 'drain') 11 12 } 13 } 14 import { createReadStream } from 'fs' import { once } from 'events' const sourceStream = createReadStream('bigdata.csv') const destStream = new SlowTransform() for await (const chunk of sourceStream) { const canContinue = destStream.write(chunk) if (!canContinue) { // backpressure, now we stop and we need to wait for drain await once(destStream, 'drain') // ok now it's safe to resume writing } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14 @loige 48

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import { pipeline } from 'stream/promises' import { createReadStream, createWriteStream } from 'fs' import { createBrotliCompress } from 'zlib' const sourceStream = createReadStream('bigdata.csv') const compress = createBrotliCompress() const destStream = createWriteStream('bigdata.csv.br') await pipeline( sourceStream, compress, destStream ) 1 2 3 4 5 6 7 8 9 10 11 12 13 import { pipeline } from 'stream/promises' 1 import { createReadStream, createWriteStream } from 'fs' 2 import { createBrotliCompress } from 'zlib' 3 4 const sourceStream = createReadStream('bigdata.csv') 5 const compress = createBrotliCompress() 6 const destStream = createWriteStream('bigdata.csv.br') 7 8 await pipeline( 9 sourceStream, 10 compress, 11 destStream 12 ) 13 import { createReadStream, createWriteStream } from 'fs' import { createBrotliCompress } from 'zlib' import { pipeline } from 'stream/promises' 1 2 3 4 const sourceStream = createReadStream('bigdata.csv') 5 const compress = createBrotliCompress() 6 const destStream = createWriteStream('bigdata.csv.br') 7 8 await pipeline( 9 sourceStream, 10 compress, 11 destStream 12 ) 13 const sourceStream = createReadStream('bigdata.csv') const compress = createBrotliCompress() const destStream = createWriteStream('bigdata.csv.br') import { pipeline } from 'stream/promises' 1 import { createReadStream, createWriteStream } from 'fs' 2 import { createBrotliCompress } from 'zlib' 3 4 5 6 7 8 await pipeline( 9 sourceStream, 10 compress, 11 destStream 12 ) 13 await pipeline( sourceStream, compress, destStream ) import { pipeline } from 'stream/promises' 1 import { createReadStream, createWriteStream } from 'fs' 2 import { createBrotliCompress } from 'zlib' 3 4 const sourceStream = createReadStream('bigdata.csv') 5 const compress = createBrotliCompress() 6 const destStream = createWriteStream('bigdata.csv.br') 7 8 9 10 11 12 13 import { pipeline } from 'stream/promises' import { createReadStream, createWriteStream } from 'fs' import { createBrotliCompress } from 'zlib' const sourceStream = createReadStream('bigdata.csv') const compress = createBrotliCompress() const destStream = createWriteStream('bigdata.csv.br') await pipeline( sourceStream, compress, destStream ) 1 2 3 4 5 6 7 8 9 10 11 12 13 @loige 50

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import { on } from 'events' import glob from 'glob' const matcher = glob('**/*.js') const ac = new global.AbortController() matcher.once('end', () => ac.abort()) try { for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { console.log(`./${filePath}`) } } catch (err) { if (!ac.signal.aborted) { console.error(err) process.exit(1) } // we ignore the AbortError } console.log('NOW WE GETTING HERE! :)') // YAY! 😻 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 const ac = new global.AbortController() import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 matcher.once('end', () => ac.abort()) import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 try { } catch (err) { // we ignore the AbortError import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 @loige 54

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import { on } from 'events' import glob from 'glob' const matcher = glob('**/*.js') const ac = new global.AbortController() matcher.once('end', () => ac.abort()) try { for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { console.log(`./${filePath}`) } } catch (err) { if (!ac.signal.aborted) { console.error(err) process.exit(1) } // we ignore the AbortError } console.log('NOW WE GETTING HERE! :)') // YAY! 😻 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 const ac = new global.AbortController() import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 matcher.once('end', () => ac.abort()) import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 try { } catch (err) { // we ignore the AbortError import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 if (!ac.signal.aborted) { console.error(err) process.exit(1) } import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 14 15 16 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 @loige 54

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import { on } from 'events' import glob from 'glob' const matcher = glob('**/*.js') const ac = new global.AbortController() matcher.once('end', () => ac.abort()) try { for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { console.log(`./${filePath}`) } } catch (err) { if (!ac.signal.aborted) { console.error(err) process.exit(1) } // we ignore the AbortError } console.log('NOW WE GETTING HERE! :)') // YAY! 😻 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 const ac = new global.AbortController() import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 matcher.once('end', () => ac.abort()) import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 try { } catch (err) { // we ignore the AbortError import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 if (!ac.signal.aborted) { console.error(err) process.exit(1) } import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 14 15 16 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 // we ignore the AbortError import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 @loige 54

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import { on } from 'events' import glob from 'glob' const matcher = glob('**/*.js') const ac = new global.AbortController() matcher.once('end', () => ac.abort()) try { for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { console.log(`./${filePath}`) } } catch (err) { if (!ac.signal.aborted) { console.error(err) process.exit(1) } // we ignore the AbortError } console.log('NOW WE GETTING HERE! :)') // YAY! 😻 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 const ac = new global.AbortController() import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 matcher.once('end', () => ac.abort()) import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 try { } catch (err) { // we ignore the AbortError import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 if (!ac.signal.aborted) { console.error(err) process.exit(1) } import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 14 15 16 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 // we ignore the AbortError import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 // we ignore the AbortError 18 } 19 20 21 @loige 54

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import { on } from 'events' import glob from 'glob' const matcher = glob('**/*.js') const ac = new global.AbortController() matcher.once('end', () => ac.abort()) try { for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { console.log(`./${filePath}`) } } catch (err) { if (!ac.signal.aborted) { console.error(err) process.exit(1) } // we ignore the AbortError } console.log('NOW WE GETTING HERE! :)') // YAY! 😻 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 const ac = new global.AbortController() import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 matcher.once('end', () => ac.abort()) import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 try { } catch (err) { // we ignore the AbortError import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 if (!ac.signal.aborted) { console.error(err) process.exit(1) } import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 14 15 16 17 // we ignore the AbortError 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 // we ignore the AbortError import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 18 } 19 20 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 21 console.log('NOW WE GETTING HERE! :)') // YAY! 😻 import { on } from 'events' 1 import glob from 'glob' 2 3 const matcher = glob('**/*.js') 4 const ac = new global.AbortController() 5 6 matcher.once('end', () => ac.abort()) 7 8 try { 9 for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { 10 console.log(`./${filePath}`) 11 } 12 } catch (err) { 13 if (!ac.signal.aborted) { 14 console.error(err) 15 process.exit(1) 16 } 17 // we ignore the AbortError 18 } 19 20 21 import { on } from 'events' import glob from 'glob' const matcher = glob('**/*.js') const ac = new global.AbortController() matcher.once('end', () => ac.abort()) try { for await (const [filePath] of on(matcher, 'match', { signal: ac.signal })) { console.log(`./${filePath}`) } } catch (err) { if (!ac.signal.aborted) { console.error(err) process.exit(1) } // we ignore the AbortError } console.log('NOW WE GETTING HERE! :)') // YAY! 😻 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 @loige 54

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