What is going on with alert("1" - - "1")

Question

I just had this in a challenge and I don't know this. How is this called, when to use this. I am not referring to the alert, just the "1"- -"1" the solution seems to be 2

Answer 1

The answer is error because you cannot stack JavaScript's operators with spaces in between ,
The code should be put this way if you want output to be 2.
alert ("1" - "-1");
This gives 2 on codes playground

Answer 2

@ Maart
Try this one to fool the console.

var a = 1;
var b = 2;
console.log ( a-=-b);
this will output 3.
and it also means (a = a -- b) in real world maths

you can also stack everything together for a clean output;

console.log (1--2);

because console.log (1 - - 2); outputs an error because of those spaces in between the characters

Answer 3

@Maart Ok edited

Answer 4

In addition to @Nomeh a double negative means positive, so 1 - - 2 is the same as 1 + 2

Answer 5

https://code.sololearn.com/W0L56Cyw1zU9/?ref=app it works on playground, and was like this on a js challenge, that's why I am confused.
Oh and also, it is OK to math string numbers without parsing them first?

Answer 6

Fair. Was explaining the basic maths behind it though. Wasn't sure if he knew about that.

Answer 7

I would say no, but it does seem to work here...