JSTalk_ScopeChains

JavaScript VM internals

EventLoop, Async and ScopeChains

by Arindam Paul / @geek_paul Amazon Campus © Amazon 2015

"When there is freedom from mechanical conditioning, there is simplicity. The classical man is just a bundle of routine, ideas and tradition. If you follow the classical pattern, you are understanding the routine, the tradition, the shadow - you are not understanding yourself." - Bruce Lee

“When you don’t know what you believe, everything becomes an argument. Everything is debatable. But when you stand for something, decisions are obvious.” ― Jason Fried, Rework

Agenda

JavaScript Interpretation and Memory Model
Compilation and Lexical Scope
Function Execution
Scope Chains
JavaScript Runtime and Event loop
Async Examples
Single Threaded parallel execution

Some Gotchas

Java ≠ JavaScript

Just like Ham ≠ Hamburger

JavaScript Base Concepts

JavaScript reads top to bottom and runs to completion.
Everything is extensible and almost everything in JavaScript is mutable.
JavaScript is functional language with closures and lamda expressions inherited from Scheme.
It is also prototypal language with objects inheriting from objects directly (inheriting this nature from Self.)
Scopes can be created only using functions (functional scope) and all variables defined in a scope are hoisted to the top of the scope.

JavaScript Types

No strong typing

Memory Allocation and Garbage Collection

Let's pretend to be the Runtime and execute the code

The Code

Compilation and Execution: Part 1

Compilation and Execution: Part 2

Compilation and Execution: Part 3

Compilation and Execution: Part 4

Garbage Collection

Closures

What happens when a function is executed outside of it's original scope chains? Moreover, what happens when a variable holds on to a function reference which get's defined in such deep function execution chain.

So What is Closure?

It is an implicit, permanent link between a function and it's scope chain..

A function definition's (lambda) hidden [[scope]] reference.

Holds the scope chain (preventing garbage collection.)
It is used and copied as the "outer environment reference" anytime the function is run.

Closure in Action

Closure in Action: Contd.

Implicit Closure

var data = "My Data!";
setTimeout(function() {
	console.log(data); // prints "My Data!"
}, 3000);

Explicit Closures

function makeAdder(n) {
   var inc = n;
   var sum = 0;
   return function add() {
      sum = sum + inc;
      return sum;
   };
}

var adder3 = makeAdder(3);

Closure Demo

Event Loop and Async Programming

Enough Slides, let's go directly to the demo and see it in Action.

And the moment when it all worked...

Questions?

"When your syntax is more beautiful, you can let the reader of your code get past the syntax and closer to the intentions"

JavaScript VM internals – EventLoop, Async and ScopeChains

arindam89

JavaScript VM internals – EventLoop, Async and ScopeChains

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