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  • JavaScript Development
  • JS Principles
    • JS Principles
      • Primitive data types
      • typeof operator
      • Scope
      • Hoisting
      • IIFE
      • Closure
      • Anonymous functions in JS
      • Conditional (ternary) operator
        • Coercion vs Conversion
      • Event-driven programming
      • Factory Function
      • JSON.stringify()
      • Strict mode
      • super() keyword
      • What are memory leaks?
      • Micro-tasks within an event loop (Summary)
      • Macro-tasks within an event loop (Summary)
      • null vs undefined
    • Memory Management
    • Advanced function concepts
      • Impure vs Pure Functions
      • Factory functions
  • JavaScript Objects & Arrays
    • Introducing JavaScript objects
      • Build-in objects
        • isNaN()
      • RegExp
        • RegExp.prototype.test()
      • String
        • String.prototype.split()
        • String.prototype.slice()
      • Objects
        • Object.assign()
        • Object.create()
        • Object.defineProperties()
        • Object.defineProperty()
        • Object.entries()
        • Object.freeze()
        • Object.getOwnPropertyNames()
        • Object.getPrototypeOf()
        • Object.isFrozen()
        • Object.isSealed()
        • Map
      • Standard built-in methods to work with Arrays
        • Array.of()
        • Array.prototype.concat()
        • Array.prototype.every()
        • Array.prototype.filter()
        • Array.prototype.find()
        • Array.prototype.findIndex()
        • Array.prototype.forEach()
        • Array.prototype.join()
        • Array.prototype.map()
        • Array.prototype.pop()
        • Array.prototype.shift()
        • Array.prototype.reverse()
        • Array.prototype.some()
        • Array.prototype.sort()
        • Array.prototype.splice()
        • Array.prototype.unshift()
        • Array.prototype.includes()
        • Array.prototype.flatMap()
      • Prototypal inheritance
        • Inheritance with the prototype chain
        • Inheriting "methods"
  • JavaScript Mid
    • JavaScript & ES
      • Arrow Function
      • Anonymous Function
      • Callbacks
      • Promises
      • var, let, and const
      • Fetch API (function)
      • Fetch API
      • Synchronous vs Asynchronous
      • Encapsulation
      • Destructuring assignment
      • call() - apply() - bind()
      • 'This' keyword
      • Functional Programming
  • Browser
    • Event-driven programming
  • TypeScript
    • The TypeScript Handbook
      • Basic Types
      • Interfaces
      • Functions
      • Literal Types
      • Unions and Intersection Types
      • Classes
      • Enums
      • Generics
      • Implements vs extends
  • Hackerrank Practices
    • Practices and examples
  • JS Math
    • Mathematical
      • JavaScript | Math.E() function
      • Math.abs( ) Method
      • Math.ceil( ) function
      • Math floor()
      • Math.imul( ) Function
      • Math log( ) Method
      • Math max()/min() Method
      • Math pow( ) Method
      • Math.sign( ) Function
      • Math sqrt( ) Method
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  1. JS Principles
  2. JS Principles

Hoisting

PreviousScopeNextIIFE

Last updated 4 years ago

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Hoisting is a term you will not find used in any normative specification prose prior to .

Conceptually, for example, a strict definition of hoisting suggests that variable and function declarations are physically moved to the top of your code. In JavaScript, Hoisting is the default behavior of moving all the declarations at the top of the scope before code execution.

Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their scope before code execution. This means that the declarations will be moved to the top of their scope but not their assignations, their assignations will remain in the same spot.

Initializations are not hoisted!

Hoisting only works for declarations, not initializations. So,

console.log(y);
var y = 13;

The above code will give undefined as output, as it is the same as writing,

var y;
console.log(y);
y = 13;

Hoisting example:

// JavaScript Hoisting Example
x = 5; // Assign 5 to x
console.log(x);
var x; // Declare x
ECMAScript® 2015 Language Specification