Applying a Function to Null in Javascript

Question

Why does the following work:

function sum(a,b) { return a + b; }
var result = sum.call(null,3,4);     // 7

Why is result defined? I am invo

Answer 1

As the MDN explained.

thisArg

The value of this provided for the call to fun. Note that this may not be the actual value seen by the method: if the method is a function in non-strict mode code, null and undefined will be replaced with the global object, and primitive values will be boxed.

Simply put it by a little code.

In the strict mode ,this is null. But in the not strict mode . this is window or global object.