What is the difference between != null and !== null?
This question already has an answer here:
The answer to the specific question about whether there's ever a case where != and !== comparisons involving null get different answers is yes :
undefined != null // false
undefined !== null // true
The rules for == and != explicitly include a clause that stipulates that null and undefined are the same.
Personally — that is, in my code — that fact is a reason for using != (or == ) when checking for null in cases where undefined should be treated the same way (which is a pretty common situation).