Question

i was wondering what was the use of setting setTimeout to a variable

scroll_timer = window.setTimeout(function () { ... 

when i can just use

window.setTimeout(function () { ... 

and is there a need to clearTimeout actually? line 2

$window.scroll(function () {
    window.clearTimeout(scroll_timer);
    scroll_timer = window.setTimeout(function () { // use a timer for performance
        if($window.scrollTop() <= top) // hide if at the top of the page
        {
            displayed = false;
            $message.fadeOut(500);
        }
        else if(displayed == false) // show if scrolling down
        {
            displayed = true;
            $message.stop(true, true).show().click(function () { $message.fadeOut(500); });
        }
    }, 100);
});

code from scroll to top in jquery

Answer 1

In the given example the effect is to “reset” the timeout.

Since the scroll event can be fired many times, you would end up with many duplicate messages displayed after a tenth of a second. If a second scroll event is called before the first one has run, we cancel the first one and set a new timeout to start a tenth of a second after the latest scroll event.