Question

I recently ran across the following [effective] syntactical construct:

d <= f && func3();

The actual construct is of the form:

d > f ? a > b ? func1() : func2() : d <= f && func3();

What is the purpose of this construct?

My best guess is that func3 will only be executed if d <= f returns falsy because of the short-circuit evaluation in the && operator, but I don’t think that makes sense given that the logic in the actual function would prevent d <= f from ever being false at that point in the code, and it’s clear from DOM-watching that func3 is being executed.

If you want to see the whole code, I found this in http://cdn.sstatic.net/js/full.js?v=9358063bfb40 as referenced by https://stackoverflow.com/faq in the moveScroller function (full function below, it’s in the line that has d <= f && j.css({...}) to reset back to a relative position).

function moveScroller() {
    var g = $("#scroller").width(),
        d = function () {
            var d = $(window).scrollTop(),
                f = $("#scroller-anchor").offset().top,
                j = $("#scroller");
            d > f ? j.height() > $(window).height() ? j.css({
                position: "fixed",
                top: "",
                bottom: "0px",
                width: g
            }) : j.css({
                position: "fixed",
                top: "0px",
                bottom: "",
                width: g
            }) : d <= f && j.css({
                position: "relative",
                top: "",
                bottom: ""
            })
        };
    $(window).scroll(d).resize(d);
    d()
}

Answer 1

If either d or f are non-numeric (NaN, non-number strings, etc) then both tests d > f and d <= f can return false.

So in the code

d > f ? a > b ? func1() : func2() : d <= f && func3();

at first glance it looks like d <= f is redundant, but it will short-circuit the execution of func3 if either d or f is non-numeric.

Ugly code!