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the RISEof async… JavaScript Jeremy Fairbank blog.jeremyfairbank.com @elpapapollo | gh/jfairbank

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We help brands excel. pushagency.io Your website, SimplyBuilt. simplybuilt.com

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“Call me maybe?”

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Async API Callback

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Callback fetchUserById(1, function(err, user) { if (err) { console.error('Could not retrieve user'); } else { console.log(user); } });

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}); }); }); }); }); }); Callback Callback Callback Callback Callback Callback

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function fetchCustomerNameForOrder(orderId, done, fail) { fetchOrder(orderId, function(err, order) { if (err) { logError(err); fail(err); } else { fetchCustomer( order.customerId, function(err, customer) { if (err) { logError(err); fail(err); } else { done(customer.name); } } ); } }); }

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function fetchCustomerNameForOrder(orderId, done, fail) { fetchOrder(orderId, function(err, order) { if (err) { logError(err); fail(err); } else { fetchCustomer( order.customerId, function(err, customer) { if (err) { logError(err); fail(err); } else { done(customer.name); } } ); } }); }

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function fetchCustomerNameForOrder(orderId, done, fail) { fetchOrder(orderId, function(err, order) { if (err) { logError(err); fail(err); } else { fetchCustomer( order.customerId, function(err, customer) { if (err) { logError(err); fail(err); } else { done(customer.name); } } ); } }); }

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Async API ?

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Promise function fetchCustomerNameForOrder(orderId) { return fetchOrder(orderId) .then(order => fetchCustomer(order.customerId)) .then(customer => customer.name); }

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.then(...) .then(...) .then(...) .then(...) .then(...) .then(...) .then(...) .then(...)

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Error Error Error Error

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function fetchCustomerNameForOrder(orderId) { return fetchOrder(orderId) .then(order => fetchCustomer(order.customerId)) .then(customer => customer.name) .catch(err => { logError(err); throw err; }); }

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Getting there…

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• Readable, synchronous program flow • Nonblocking • Use native flow control constructs

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async function fetchCustomerNameForOrder(orderId) { try { const order = await fetchOrder(orderId); const customer = await fetchCustomer(order.customerId); return customer.name; } catch (err) { logError(err); throw err; } }

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async function fetchCustomerNameForOrder(orderId) { try { const order = await fetchOrder(orderId); const customer = await fetchCustomer(order.customerId); return customer.name; } catch (err) { logError(err); throw err; } }

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async function fetchCustomerNameForOrder(orderId) { try { const order = await fetchOrder(orderId); const customer = await fetchCustomer(order.customerId); return customer.name; } catch (err) { logError(err); throw err; } }

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async function fetchCustomerNameForOrder(orderId) { try { const order = await fetchOrder(orderId); const customer = await fetchCustomer(order.customerId); return customer.name; } catch (err) { logError(err); throw err; } }

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Await

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function fetchOrder(orderId) { return fetch(`/orders/${orderId}`) .then(response => response.json()); } function printOrder(orderId) { fetchOrder(orderId) .then(order => console.log(order)); }

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function fetchOrder(orderId) { return fetch(`/orders/${orderId}`) .then(response => response.json()); } async function printOrder(orderId) { const order = await fetchOrder(orderId); console.log(order); }

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async printOrder(orderId) { const order = await fetchOrder(orderId); console.log(order); } fetchOrder(orderId) order

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async printOrder(orderId) { const order = await fetchOrder(orderId); console.log(order); } await

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async printOrder(orderId) { const order = await fetchOrder(orderId); console.log(order); } await order

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await order

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await order

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async printOrder(orderId) { const order = await fetchOrder(orderId); console.log(order); } ?

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async function printOrder(orderId) { const order = await fetchOrder(orderId); console.log(order); } printOrder(1); Invoke

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async function printOrder(orderId) { const order = await fetchOrder(orderId); console.log(order); } printOrder(1); Encounter await

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async function printOrder(orderId) { const order = await fetchOrder(orderId); console.log(order); } printOrder(1); Wrap in Promise.resolve

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Wrap in Promise.resolve async function printOrder(orderId) { const promise = Promise.resolve(fetchOrder(orderId)); console.log(order); } printOrder(1);

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async function printOrder(orderId) { const promise = Promise.resolve(fetchOrder(orderId)); console.log(order); } printOrder(1); Wrap rest with then callback

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async function printOrder(orderId) { const promise = Promise.resolve(fetchOrder(orderId)); return promise.then(order => { console.log(order); return Promise.resolve(undefined); }); } printOrder(1); Wrap rest with then callback

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async function printOrder(orderId) { const promise = Promise.resolve(fetchOrder(orderId)); return promise.then(order => { console.log(order); return Promise.resolve(undefined); }); } printOrder(1); Wrap implicit return with Promise.resolve

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function fetchCustomerNameForOrder(orderId) { return Promise.resolve(fetchOrder(orderId)) .then(order => { return Promise.resolve(fetchCustomer(order.customerId)) .then(customer => { return Promise.resolve(customer.name); }); }); } ?

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async function meaningOfLife() { return 42; } meaningOfLife() === 42; ???

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async function meaningOfLife() { return 42; } function meaningOfLife() { return Promise.resolve(42); } meaningOfLife() .then(answer => answer === 42);

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Exceptional Situations

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async function printOrder(orderId) { try { const order = await fetchOrder(orderId); console.log(order); } catch (e) { console.log('Error retrieving order', e); } }

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async function printOrder(orderId) { try { const order = await fetchOrder(orderId); console.log(order); } catch (e) { console.log('Error retrieving order', e); } } ?

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function fetchOrder(orderId) { return fetch(`/orders/${orderId}`) .then(resp => { if (resp.status === 404) { throw new Error('Order not found'); } return resp.json(); }); }

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function fetchOrder(orderId) { return new Promise((resolve, reject) => { $.get(`/orders/${orderId}`) .done(order => resolve(order)) .fail(resp => { if (resp.status === 404) { reject(new Error('Order not found')); } }); }); }

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Error Error Error Error

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Regain Control

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async function findOrCreateOrder(orderId) { let order; if (await orderExists(orderId)) { order = await fetchOrder(orderId); } else { order = await createOrder(); } return order; }

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async function findOrCreateOrder(orderId) { let order; if (await orderExists(orderId)) { order = await fetchOrder(orderId); } else { order = await createOrder(); } return order; }

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async function printOrders(orderIds) { for (const id of orderIds) { const order = await fetchOrder(id); console.log(order); } }

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async function printOrders(orderIds) { for (const id of orderIds) { const order = await fetchOrder(id); console.log(order); } }

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async function printOrders(orderIds) { for (const id of orderIds) { const order = await fetchOrder(id); console.log(order); } } Problem?

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async function printOrders(orderIds) { for (const id of orderIds) { const order = await fetchOrder(id); console.log(order); } } printOrders([1, 2, 3]);

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printOrders([1, 2, 3]); await fetchOrder(1); await fetchOrder(2); await fetchOrder(3);

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printOrders([1, 2, 3]); await fetchOrder(1); await fetchOrder(2); await fetchOrder(3);

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printOrders([1, 2, 3]); await fetchOrder(1); await fetchOrder(2); await fetchOrder(3);

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async function printOrders(orderIds) { const orders = await Promise.all( orderIds.map(fetchOrder) ); orders.forEach(order => console.log(order)); }

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async function printOrders(orderIds) { const orders = await Promise.all( orderIds.map(fetchOrder) ); orders.forEach(order => console.log(order)); }

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printOrders([1, 2, 3]); await Promise.all([ fetchOrder(1), fetchOrder(2), fetchOrder(3) ]);

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printOrders([1, 2, 3]); Demo rise.of.async.jeremyfairbank.com

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$ npm install --save-dev \ babel-core \ babel-cli \ babel-preset-es2015 \ babel-plugin-syntax-async-functions \ babel-plugin-transform-regenerator \ babel-plugin-transform-runtime

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.babelrc { "presets": ["es2015"], "plugins": [ "syntax-async-functions", "transform-regenerator", "transform-runtime" ] }

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$ node_modules/.bin/babel-node myAsyncFile.js

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• tc39.github.io/ecmascript-asyncawait/ • github.com/tc39/ecmascript-asyncawait • github.com/tc39/ecma262 Resources

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THANKS! Jeremy Fairbank blog.jeremyfairbank.com @elpapapollo | gh/jfairbank speakerdeck.com/jfairbank/fluent-conf-rise-of-async-javascript SLIDES: github.com/jfairbank/rise-of-async-js-talk CODE: