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