JavaScript- Scopes and Closures

Scope

The scope is the set of variables, objects, and functions you have access to.

Create Scope

Use functions

Declaring Variables

If you do write operation without declaring variable -> work fine

foo = 10; console.log(foo); -> 10

If you do read operation without declaring variable -> doesn't work fine

console.log(foo) -> syntax error

Window Object

Inbuilt object provided by JavaScript itself
Every global variable and functions are part of window object

JavaScript is both compilations and interpreted language

Compilation: register variables, method names, arguments in global scope
Interpretation: assign values to global scope and execute the code
global scope problem: undeclared function inside the variable it goes to global scope

Hoisting

It doesn't matter where you declare your variable (In the compilation step it include all variables automatically before the interpretation)

Strict Mode

To get strict mode: "use strict"
It doesn't allow use variables without declaring it before.

Closure

Function remembers it's declaration scope at every stage when it executes

Callback

setTimeout(function,time)
The function you want to execute after waiting defined time(milliseconds)

Important Facts

JavaScript is not block scoping language: {} doesn't create blocks in JavaScript
IIFE: Immediately Invoke Function Expressions

Execute anonymous functions directly

When executing functions each time new copy of local variables are produce

GitHub repo: https://github.com/kaosadi17/JavaScript/blob/master/scopes%26Closures.js

Comments

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