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Hoisting is a term you will not find in the JavaScript docs. Hoisting was thought up as a general way of thinking about how execution context (specifically the creation and execution phases) work in JavaScript. But, hoisting can lead to misunderstandings. For example, hoisting teaches that variable and function declarations are physically moved to the top your coding, but this is not what happens at all. What does happen is the variable and function declarations are put into memory during the compile phase, but stays exactly where you typed it in your coding.  

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Technical example

One of the advantages you get from JavaScript putting function declarations into memory first, before it executes any coding, is this allows you to use a function before you declare it in your coding. For example:

function catName(name) {
  console.log("My cat's name is " + name);
}

catName("Tigger");
/*
The result of the code above is: "My cat's name is Tigger"
*/

The above coding is how you would expect to write the coding for it to work. Now, lets see what happens when we call the function in our coding before we write it:

catName("Chloe");

function catName(name) {
  console.log("My cat's name is " + name);
}
/*
The result of the code above is: "My cat's name is Chloe"
*/

Even though we call the function in our coding first, before the function is written, the coding still works. This is in thanks to how context execution works in JavaScript.

Hoisting works well with other data types and variables  as well. The variables can be initialized and used before declared. But they cannot be used without initialization. 

Technical example
 

num = 6;
num + 7;
var num; 
/* gives no errors as long as num is declared*/

JavaScript only hoists declarations, not initializations. If you were to use a variable that is declared and initialized after using, the value will be undefined. The below two examples demonstrate the same behavior.
 

var x = 1; // Initialize x
console.log(x + " " + y);  //y is undefined
var y = 2;
//the above code and the below code are the same

var x = 1; // Initialize x
var y; // Declare y
console.log(x + " " + y);  //y is undefined
y = 2; // Initialize y

 

 

Technical reference

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 Last updated by: mhalitk,