Strict Mode in Javascript.

Question

when i use the strict mode the output is false but without strict mode the output is true why?

"use strict";
function myFun(){
console.log(this==window);//it refers to the window object
}
myFun();

Answer 1

When strict mode is enabled "this" points to an undefined value if used within a function.
undefined == window //false

Such behavior prevents the silent creation of global variables this way:

function bad(){
this.sth = 42; //now sth is global
..... //more code
}
var object = bad(); //You shouldn't call a constructor without the "new" keyword. Why? See line below↓
console.log(sth); //42 oops

When strict mode is enabled you will be forced to use the new keyword. That's a good practice, strict mode enabled or not.
Hope this helps.