Hoisting is JavaScript's default behavior of moving declarations to the top.
In JavaScript, Declearations are hoisted not initilisations
Ex:
var x = 5; // Initialize x
elem = document.getElementById("demo"); // Find an element elem.innerHTML = x + " " + y; // Display x and y
var y = 7; // Initialize y
Here y is undefined, thats because only the declaration (var y), not the initialisation (=7) is hoisted to the top.