What does `!!~` mean in javascript? [duplicate]

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

There's a specfic reason you'll sometimes see ~ applied in front of $.inArray.

Basically,

~$.inArray("foo", bar) 

is a shorter way to do

$.inArray("foo", bar) !== -1 

$.inArray returns the index of the item in the array if the first argument is found, and it returns -1 if its not found. This means that if you're looking for a boolean of "is this value in the array?", you can't do a boolean comparison, since -1 is a truthy value, and when $.inArray returns 0 (a falsy value), it means its actually found in the first element of the array.

Applying the ~ bitwise operator causes -1 to become 0, and causes 0 to become `-1. Thus, not finding the value in the array and applying the bitwise NOT results in a falsy value (0), and all other values will return non-0 numbers, and will represent a truthy result.

if (~$.inArray("foo", ["foo",2,3])) {     // Will run } 

And it'll work as intended.