Exactly what @damjan said. It just converts true to 1 and false to 0. Today I would probably use the + operator: +/.../.test(...) just to save another character :-)

Check out this StackOverflow thread. Basically, ~ is the bitwise NOT operator, and applying it twice converts anything to an integer. It's used in this answer to convert the output of RegExp.test from a boolean to a number. Example: ~~true === 1. You will more often see it used to truncate anything after the decimal point, as a sort of floor function.