Question

undefined === null => false
undefined == null => true

1. I have thought about the reason of undefined == null and found out only one case:

   if(document.getElementById() == null) ....
   

   Is there any other reason to make (undefined === null) == false ?

2. Is there any other examples of use === – operation in javascript?

Answer 1

Is there any other reason to make (undefined === null) == false ?

They are not equal so the Strict Equality Comparison Algorithm considers them to be false.

Is there any other examples of use === – operation in javascript?

The === gives the most predictable result. I only use == when I have a specific purpose for type coercion. (See Abstract Equality Comparison Algorithm.)