Hoisting

Allows us to access functions and variables before they are created.

2 things that are hoisted in JavaScript:

Function declarations

Variable declarations

Function hoisting

sayHi();

function sayHi() {
  console.log('Hi');
}

// Output - Hi

The above happens because when we run the JavaScript file, JavaScript compiler will take all function declarations and move them to the top of the file available for use.

Suggestion: Always define functions before using them.

Note: Functions made using a variable are not hoisted.

add(10,20);

const add = function(a,b) {
	return a + b;
}

//Output - Uncaught ReferenceError: Cannot access 'add' before initialization

Variable hoisting

console.log(age);
var age = 10;

// Output - undefined

This happens because JavaScript hoists the variable declaration but not the actual setting of the values or assignment. This essentially means this happens:

var age;
console.log(age);
age = 10;

// Output - undefined