I saw this code:
this.vertical = vertical !== undefined ? !!vertical : this.vertical;
It seems to be using !!
as an operator, which I don't recognize. What does it do?
It converts Object
to boolean
. If it was falsy (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 is generally 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