What is Hoisting in JavaScript?

Hoisting is the JavaScript interpreter’s action of moving all variable and function declarations to the top of the current scope. There are two types of hoisting:

• variable hoisting – rare
• function hoisting – more common

Wherever a var (or function declaration) appears inside a scope, that declaration is taken to belong to the entire scope and accessible everywhere throughout.

var a = 2;
foo();				   // works because `foo()`
						 // declaration is "hoisted"

function foo() {
	a = 3;
	console.log( a );	// 3
	var a;			   // declaration is "hoisted"
					     // to the top of `foo()`
}

console.log( a );	// 2