Strange code in jQuery sources: var !== var ? x : y;

Question

Recently I found one weird line in the jQuery sources (last version 1.9.1, Sizzle package, line 129 funescape function):

funescape = function( _         


        

Answer 1

I'm piggy-backing on some of the comments here, but think this worthy information.

Some comments on the original question have suggested that this method of checking for NaN is actually much faster than isNaN()

When taken in conjunction with the following alternative to parseInt parseFloat we have a very fast way of converting to a number and checking its numeric state.

Is Subtracting Zero some sort of JavaScript performance trick?

So instead of

function Translated(val) {
    var x = parseFloat(val);
    if (!isNaN(x)) {
        alert("Not a number");
    }
}

We can have

function WTF(val) {
    var x = val - 0;
    if (x !== x) {
        alert("Not a number");
    }
}