Javascript String Assignment Operators

Question

How come I can use += on a string, but I cannot use -= on it?

For example...

var test = \"Test\";
var arr = \"⇔\"         


        

Answer 1

The short answer is - it isn't defined to work with strings.

Longer answer: if you try the subtraction operator on two strings, it will first cast them to numbers and then perform the arithmetic.

"10" - "2" = 8

If you try something that is non-numeric, you get a NaN related error:

"AA" - "A" = NaN