!!
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
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