Javascript - Why isNaN(1 + null) returns false?

Question

Well,I am going through Mozilla Javascript Reference and found that..

isNaN(1 + null) //false
isNaN(1 + undefined) //true

I am not able to understand reason behind this.

Have you tried printing just the value of `1 + null`? That's the base reason. — JJJ, Mar 07 '17 at 07:15

score 6 · Accepted Answer · edited Mar 07 '17 at 07:25

6

From https://www.w3schools.com/js/js_type_conversion.asp, , when null is converted to number, it becomes 0. Therefore, 0 + 1 = 1, it's valid number, so isNaN returns false.

When undefined is converted to Number, it becomes NaN. Any Number + NaN = NaN, so isNaN return true.

edited Mar 07 '17 at 07:25

Sagar V

answered Mar 07 '17 at 07:16

Nikita Shaposhnik

5

Upvoted, but instead of w3schools, you can reference something more accurate: https://www.ecma-international.org/ecma-262/6.0/#sec-tonumber – Gerardo Furtado Mar 07 '17 at 07:17
@niki thanks for explaining this. – mukesh kudi Mar 07 '17 at 07:33

1 Answers1