Why does "1" - - "1" return 2?

Question

Why does alert("1" - - "1") return 2?

I'm not entirely sure what is going on here to create the result as 2?

I came across the problem here: http://davidshariff.com/js-quiz

prefix unary `-` tries to convert its operand to a number. That results in `-1`. If you subtract -1 from 1, again, the binary infix `-` operator will try to convert its argument as well, so you end up with `1 - (-1)` which is 2. — The Paramagnetic Croissant, Nov 24 '14 at 21:27

score 3 · Accepted Answer · edited May 23 '17 at 12:21

3

it's like writing 1 - (-1) which is 1 + 1 = 2

the problem in js is that if you use + between 2 string it means concating them thus resulting 11

EDIT: thanks to iamnotmaynard comment i was able to find this post

edited May 23 '17 at 12:21

Community

answered Nov 24 '14 at 21:28

ymz

This only answers part of the question. There is also confusion about type coercion. – Reinstate Monica -- notmaynard Nov 24 '14 at 21:29
When you use the "-" infix, javascript assumes that both of the arguments are numbers. For every other data type this operation does not make any sense. So if it is a string it tries to parse it as a number. You can try "test" - "something". This will return NaN. – Schnodderbalken Nov 24 '14 at 21:33

1 Answers1