Edit in JSFiddle

var a = new Array(5);
var b = [undefined,undefined,undefined,undefined,undefined];
console.log("a[0]: " +  a[0]);
console.log("b[0]: " + b[0]);
console.log("a[4]: " + a[4]);
console.log("b[4]: " + b[4]);
console.log("b[2]===a[2]: " + (b[2]===a[2]));
console.log("a===b: " + (a===b));
console.log("a==b: "+ (a==b));
a.map(function() { console.log("Hallo from a array") });
b.map(function() { console.log("Hallo from b array") });