It converts Object to boolean. If it was falsey (e.g., 0, null, undefined, etc.), it would be false, otherwise, true.
!object // Inverted Boolean
!!object // Noninverted Boolean, so true Boolean representation
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