While reading a book, I came across this code snippet:
!!(document.all && document.uniqueID);
I'm wondering why the double not operator is used here. Doesn't the && operator already convert the result to a Boolean?
While reading a book, I came across this code snippet:
!!(document.all && document.uniqueID);
I'm wondering why the double not operator is used here. Doesn't the && operator already convert the result to a Boolean?
&& will give back the value of document.uniqueID (assuming that document.all is not equal to '',false, null, undefined, 0, NaN) for
document.all && document.uniqueID For instance 45 === (true && 45) //true
Referenced from mozilla.org.
Logical AND (&&) expr1 && expr2 gives back expr1 if it can be converted to false; otherwise, it returns expr2. Hence, when used with Boolean values, && gives true only if both operands are true; else, it gives false.
That's why it is important to apply !! to convert the above expression into a Boolean value.
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