What is the "!!" operator in Javascript?
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What is the !! operator in JavaScript?
Sorry if this one is obvious but I can't google it
What is the "!!" operator in Javascript? eg
if (!!window.EventSource) { var source = new EventSource('stream.php'); } else { // Result to xhr polling :( }
Did the author just use "!" twice ie a double negation? I'm confused because this is in the official doc
It will convert anything to true or false :
!!0 // => false
!!1 // => true
!!'a' // => true
!!'' // => false
!!null // => false
Technically, !! is not an operator, it is just two ! operators next to each other. But a double-negation is pointless unless you are using !! like an operator to convert to Boolean type.
In most languages, !! is double negation, as ! is negation. Consider this:
# We know that...
!false == true
# And therefore...
!!false == false
!!true == true
It's often used to check whether a value exists and is not false, as such:
!!'some string' == true
!!123 == true
!!myVar == true
!! is used to convert a non-zero/non-null value to boolean true and a zero/null value to false.
Eg if a = 4, then !a = false and !!a = !(!a) = true.
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