Strict Mode JavaScript

normal.js

var lastName = '';
// some code here
// at later point
lastNam = 'Nagarajan'; // value will be assigned to window.lastNam
alert(lastName);
alert(window.lastNam);

strict.js

"use strict";
var lastName = '';
// some code here
// at later point
lastNam = 'Nagarajan'; // this will throw ReferenceError in strict mode
alert(lastName);