Convert any type into boolean — JS

!!

it’s used to convert something to boolean

Converts Object to boolean. If it was falsy (e.g. 0, null, undefined, etc.), it will be false, otherwise, true.

So !! is not an operator, it's just the ! operator twice.

It may be simpler to do:

Boolean(object) // boolean

Real-World Example “Test IE version”:

const isIE8 = !! navigator.userAgent.match(/MSIE 8.0/);  
console.log(isIE8); // returns true or false

If you ⇒

console.log(navigator.userAgent.match(/MSIE 8.0/));  
// returns either an Array or null

But if you ⇒

console.log(!!navigator.userAgent.match(/MSIE 8.0/));  
// returns either true or false