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What is the !! operator in JavaScript?
What does !! (double exclamation point) mean?
I am going through some custom JavaScript code at my workplace and I am not able to understand the following construct.
var myThemeKey = (!!$('row') && $('row').hasClassName('green-theme')) ? 'green' : 'white'; I understand everything on the above line except !! operator. I assume that it is a NOT operator and NOT of NOT is the original value but why would someone do a NOT of NOT?
Can someone please help me understand what is happening on the above line of code?
81 Answer
The !! ensures the resulting type is a boolean (true or false).
javascript:alert("foo") --> foo
javascript:alert(!"foo") --> false
javascript:alert(!!"foo") --> true
javascript:alert(!!null) --> false
They do this to make sure $('row') isn't null.
It's shorter to type than $('row') != null ? true : false.
