Dissecting Node.js – Understanding the most famous JS runtime to the bare bone

by Lucas Santos

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Dissecting Node.js Understanding the most popular JS runtime... To the bone

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whoami /khaosdoctor @_staticvoid lsantos.dev /khaosdoctor cloud advocate_ [email protected]

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obarra.co trainingcenter.io

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abcdevelopers.org

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agenda_ - What is JavaScript - What is Node.js - Our little function - How JavaScript works - V8 and its sorceries - V8 compiling pipelines - Putting it all together

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what is JavaScript?

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JavaScript The language everyone loves to hate - Prototype-based - Dynamically-typed - Interpreted language - Created in 1995 as a scripting language for Netscape - Created by Brendan Eich - Conforms with ECMA262 (ECMAScript) - Deﬁned/Maintained by TC39

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what is Node.js?

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Node.js The angel that brought JS to the world again - JavaScript server-side runtime - Created in 2009 by Ryan Dahl - Later sponsored by Joyent - Event loop - Non blocking I/O - Uses V8

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elements of Node.js_

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our little function_

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fs is a C++ binding_

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the real Node.js_

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how JavaScript works?

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the JS engine_

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What is an engine? - Runs all JS code we write - Responsible for - parsing and interpreting - memory allocation - the call stack - garbage collection - code optimizations

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There are many - V8 -> made by Google for Chrome and some Chromium-based browsers - Chakra -> made by Microsoft for Microsoft Edge - SpiderMonkey -> made by Netscape, now runs on Firefox - Rhino -> made by Mozilla, in Java - Nitro -> made by Apple for Safari - JerryScript, Espruino -> IoT - And many others...

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Simpliﬁed diagram of an engine

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JavaScript is single-threaded_

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what means to be single-threaded? - We only have one call stack - We can only run one thing at a time

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call stack?

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call stack - Not part of JS - Provided by V8 - Data structure - Ordered as LIFO - Keeps track of function calls - Made of stack frames

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Call Stack Step 0

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Call Stack Step 1 printSquare(5)

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Call Stack Step 2 printSquare(5) multiply(x, x)

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Call Stack Step 2 printSquare(5)

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Call Stack Step 3 printSquare(5) console.log(s)

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Call Stack Step 4 printSquare(5)

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Call Stack Step 5

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stack overﬂow

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Call Stack f() f() f() f() f() f() f() f() f()

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the hosting environment_

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hosting environment - Wherever place the code is running on - Provides external APIs - Handles async queues

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the real diagram

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event loop

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callbacks

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event loop - Handle async code - Puts queued callbacks onto the call stack - In Node, provided by libuv - Not part of V8 - Not part of JS

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libuv

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libuv more than an event loop - Open source - Created for node - Wrapper around libev - Provides - Event loop - TCP & UDP - DNS Resolution - FS Events - IPC and Child processes - Thread pool - More...

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callback queues_

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async callback function

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Call Stack Ext. APIs CB queue

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Call Stack Ext. APIs CB queue console.log('Starting')

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Call Stack Ext. APIs CB queue console.log('Starting') Starting

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Call Stack Ext. APIs CB queue

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Call Stack Ext. APIs CB queue fs.readFile(fp, cb)

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Call Stack Ext. APIs CB queue fs.readFile(fp, cb) file cb

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Call Stack Ext. APIs CB queue file cb

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Call Stack Ext. APIs CB queue file cb console.log('Ending')

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Call Stack Ext. APIs CB queue console.log('Ending') Starting Ending cb

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later does not mean "later"

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Call Stack Ext. APIs CB queue cb

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Call Stack Ext. APIs CB queue cb(err, data)

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Call Stack Ext. APIs CB queue cb(err, data) console.log(data.toS())

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Call Stack Ext. APIs CB queue Starting Ending The file contents cb(err, data) console.log(data.toS())

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Call Stack Ext. APIs CB queue cb(err, data)

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Call Stack Ext. APIs CB queue

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microtasks and macrotasks_

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microtask queue

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microtasks - process.nextTick - Promises - Object.observe

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macrotask queue

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macrotasks - setTimeout - setInterval - setImmediate - any I/O operation

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what would happen?

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Call Stack Ext. APIs CB queue Job queue console.log('start')

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Call Stack Ext. APIs CB queue Job queue console.log('start') start

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Call Stack Ext. APIs CB queue Job queue

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Call Stack Ext. APIs CB queue Job queue setTimeout('t1',0)

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Call Stack Ext. APIs CB queue Job queue setTimeout('t1',0) timer cb1

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Call Stack Ext. APIs CB queue Job queue timer cb1

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Call Stack Ext. APIs CB queue Job queue setTimeout('t2',0) timer cb1

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Call Stack Ext. APIs CB queue Job queue setTimeout('t2',0) timer cb1 timer cb2

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Call Stack Ext. APIs CB queue Job queue timer cb1 timer cb2

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Call Stack Ext. APIs CB queue Job queue timer cb2 .then(console.log) cb1

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Call Stack Ext. APIs CB queue Job queue handle setTimeout('t3',0) cb1 cb2

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Call Stack Ext. APIs CB queue Job queue timer cb3 handle setTimeout('t3',0) cb1 cb2

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Call Stack Ext. APIs CB queue Job queue handle .then(fn) cb1 cb2 cb3

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Call Stack Ext. APIs CB queue Job queue handle .then(fn) fn cb1 cb2 cb3

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Call Stack Ext. APIs CB queue Job queue handle fn cb1 cb2 cb3

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Call Stack Ext. APIs CB queue Job queue handle fn cb1 cb2 cb3

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Call Stack Ext. APIs CB queue Job queue handle fn setTimeout('tp',0) cb1 cb2 cb3

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Call Stack Ext. APIs CB queue Job queue timer cb4 handle fn setTimeout('tp',0) cb1 cb2 cb3

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Call Stack Ext. APIs CB queue Job queue timer cb4 handle fn cb1 cb2 cb3

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Call Stack Ext. APIs CB queue Job queue timer cb4 fn cb1 cb2 cb3

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Call Stack Ext. APIs CB queue Job queue fn cb1 cb2 cb3 cb4

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Call Stack Ext. APIs CB queue Job queue fn console.log('promise') cb1 cb2 cb3 cb4

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Call Stack Ext. APIs CB queue Job queue fn console.log('promise') start promise cb1 cb2 cb3 cb4

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Call Stack Ext. APIs CB queue Job queue fn cb1 cb2 cb3 cb4

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Call Stack Ext. APIs CB queue Job queue cb1 cb2 cb3 cb4

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Call Stack Ext. APIs CB queue Job queue cb2 cb3 cb4 cb1

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Call Stack Ext. APIs CB queue Job queue cb2 cb3 cb4 cb1 console.log('timeout')

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Call Stack Ext. APIs CB queue Job queue cb2 cb3 cb4 cb1 console.log('timeout') start promise timeout

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Call Stack Ext. APIs CB queue Job queue cb2 cb3 cb4 cb1

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Call Stack Ext. APIs CB queue Job queue cb2 cb3 cb4

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Call Stack Ext. APIs CB queue Job queue cb3 cb4 cb2

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Call Stack Ext. APIs CB queue Job queue cb3 cb4 cb2 console.log('timeout2')

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Call Stack Ext. APIs CB queue Job queue cb3 cb4 cb2 console.log('timeout2') start promise timeout timeout2

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Call Stack Ext. APIs CB queue Job queue cb3 cb4 cb2

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Call Stack Ext. APIs CB queue Job queue cb3 cb4

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Call Stack Ext. APIs CB queue Job queue cb4 cb3

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Call Stack Ext. APIs CB queue Job queue cb4 cb3 console.log('timeout3')

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Call Stack Ext. APIs CB queue Job queue cb4 cb3 console.log('timeout3') start promise timeout timeout2 timeout3

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Call Stack Ext. APIs CB queue Job queue cb4 cb3

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Call Stack Ext. APIs CB queue Job queue cb4

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Call Stack Ext. APIs CB queue Job queue cb4

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Call Stack Ext. APIs CB queue Job queue cb4 console.log('p timeout')

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Call Stack Ext. APIs CB queue Job queue cb4 console.log('p timeout') start promise timeout timeout2 timeout3 promise timeout

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Call Stack Ext. APIs CB queue Job queue cb4

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Call Stack Ext. APIs CB queue Job queue

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V8 the golden compiler - Made by Google - open source high-performance - JS and WebAsm engine - Written in C++ - Implements ES fully - Can be standalone

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abstract syntax tree_

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AST of readFile (part)

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hidden classes_

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property order matters_

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V8 pipelines_

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AoT vs JiT

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old compiler pipeline_

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Full-Codegen

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FCG compiler fast, but not that good - First step of the pipeline - Simple and fast - Not-optimised, relatively slow - Handles type-feedback, ﬁnds hot functions - Takes the AST and generate generic native code

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Crankshaft

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Crankshaft compiler good, but not that fast - Takes type-feedback from FCG - Optimises code accordingly - Replaces not-opt code with optimised code using OSR - Does not implement all ES - Made of two components - Hydrogen - Lithium

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new compiler pipeline_

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new compiler pipeline

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TurboFan

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TurboFan Crankshaft, the right way - Started as a secondary compiler for ES6 - Designed to be a webasm compiler - Uses a sea of nodes - Receives bytecodes directly - Divided in layers - Frontend - Optimising Layer - Backend - Fixed deoptimisation cliﬀs

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mixed old pipeline

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current pipeline

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Ignition

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Ignition an interpreter to rule them all - JS Interpreter - Generates optimised bytecode - Created to reduce memory usage - Focused on low memory devices (cell phones) - NOT a parser - AST not source of truth anymore - Uses Turbofan's backend

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ignition pipeline_

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bytecodes

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bytecodes are middle-class representations

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node --print-bytecode --print-bytecode-ﬁlter=f index.js

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putting it all together_

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generated bytecode for readFileAsync

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Goes through this pipeline

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Call Stack Ext. APIs CB queue Job queue

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Call Stack Ext. APIs CB queue Job queue path.resolve

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Call Stack Ext. APIs CB queue Job queue

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Call Stack Ext. APIs CB queue Job queue IIFE

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Call Stack Ext. APIs CB queue Job queue IIFE readFileAsync

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Call Stack Ext. APIs CB queue Job queue handle IIFE

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Call Stack Ext. APIs CB queue Job queue handle

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Call Stack Ext. APIs CB queue Job queue handle

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Call Stack Ext. APIs CB queue Job queue handle readFile

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Call Stack Ext. APIs CB queue Job queue handle file cb

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Call Stack Ext. APIs CB queue Job queue cb

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Call Stack Ext. APIs CB queue Job queue cb

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Call Stack Ext. APIs CB queue Job queue cb resolve

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Call Stack Ext. APIs CB queue Job queue cb resolve callback

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Call Stack Ext. APIs CB queue Job queue cb resolve callback toString()

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Call Stack Ext. APIs CB queue Job queue cb resolve callback

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Call Stack Ext. APIs CB queue Job queue cb resolve

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Call Stack Ext. APIs CB queue Job queue cb

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Call Stack Ext. APIs CB queue Job queue cb console.log

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Call Stack Ext. APIs CB queue Job queue cb

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Call Stack Ext. APIs CB queue Job queue

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references_ - All references are in this guide: bit.ly/node-under-the-hood

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references_ - https://dev.to/khaosdoctor/node-js-under-the-hood-1-getting-to-know-our-tools-1465 - https://dev.to/khaosdoctor/node-js-under-the-hood-2-understanding-javascript-48cn - https://dev.to/khaosdoctor/node-js-under-the-hood-3-deep-dive-into-the-event-loop-135d - https://dev.to/khaosdoctor/node-js-under-the-hood-4-let-s-talk-about-v8-1eol - https://dev.to/khaosdoctor/node-js-under-the-hood-5-hidden-classes-variable-allocations-1244 - https://dev.to/khaosdoctor/node-js-under-the-hood-6-the-old-v8-34hm - https://dev.to/khaosdoctor/node-js-under-the-hood-7-the-new-v8-4gd6 - https://dev.to/khaosdoctor/node-js-under-the-hood-8-oh-the-bytecodes-1p6p - https://dev.to/khaosdoctor/node-js-under-the-hood-9-collecting-the-garbage-772

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thank you :D /khaosdoctor @_staticvoid lsantos.dev /khaosdoctor