+!! operator in an if statement

Question

I was reviewing the code for an angularjs factory to better understand how it works. The code contains an if statement that I don\'t fully understand.

I

Answer 1

This is a horribly unreadable way to write out the boolean value of a variable, and then convert it using unary conversion to give a 0/1 number result.

Consider:

+!!true; //this converts true to false, then to true again, and true is 1 when converted
+!!0; //converts 0 (falsy) to true, then false, and then the numeric 0

Technically speaking !! is not its own operator, it's just the NOT (!) operator twice.

Unary conversion: ECMA spec doc a unary plus attempts to convert to an integer. Number() would also be a valid conversion.