How does !!~ (not not tilde/bang bang tilde) alter

Question

If you read the comments at the jQuery inArray page here, there's an interesting declaration:

!!~jQuery.inArray(elm, arr) 

Now, I believe a double-exclamation point will convert the result to type boolean, with the value of true. What I don't understand is what is the use of the tilde (~) operator in all of this?

var arr = ["one", "two", "three"];
if (jQuery.inArray("one", arr) > -1) { alert("Found"); }

Refactoring the if statement:

if (!!~jQuery.inArray("one", arr)) { alert("Found"); }

Breakdown:

jQuery.inArray("one", arr)     // 0
~jQuery.inArray("one", arr)    // -1 (why?)
!~jQuery.inArray("one", arr)   // false
!!~jQuery.inArray("one", arr)  // true

I also noticed that if I put the tilde in front, the result is -2.

~!!~jQuery.inArray("one", arr) // -2

I don't understand the purpose of the tilde here. Can someone please explain it or point me towards a resource?

Answer 1

You're right: This code will return false when the indexOf call returns -1; otherwise true.

As you say, it would be much more sensible to use something like

return this.modifiedPaths.indexOf(path) !== -1;