How to call a function after scroll has ended?

Question

I want to call a function right after a scroll ends. I have tried a load of different things, none of which have quite worked, and then I came upon this solution in SO:

How do I know when I've stopped scrolling Javascript

I took a good look at the second answer and tried it - it works. Then I tried to change it slightly for my purposes. So now the whole shebang looks like this:

<!DOCTYPE html>
<html>

<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<title>Do something after scroll ends</title>

<style type="text/css">
    #scrollableDiv{
        width:500px;
        height:100px;
        overflow:scroll;
    }

    #someContent{
        width:600px;
        height:200px;
    }
</style>

<script type="text/javascript" src="scripts/jquery-1.5.1-min.js"></script>

<script type="text/javascript">
    $(document).ready(function() {

        $('#scrollableDiv').bind('scroll', bodyScroll);

        var scrollTimer = -1;

        function bodyScroll() {
            console.log('scrolling.');

            if (scrollTimer != -1)
                clearTimeout(scrollTimer);

            scrollTimer = window.setTimeout('scrollEnded()', 500);

        };

        function scrollEnded(){
            console.log('scrollEnded. Now do something astounding.');
        };

    });
</script>

</head>

<body>

<div id="scrollableDiv">
    <div id="someContent">
        Scroll me.  
    </div>
</div>

</body>
</html>

When I run this, the scroll event triggers (great!).

Then, instead of calling my "scrollEnded()" function, an error is generated: "scrollEnded is not defined". I've tried to figure out where this comes from by going into debug mode and stepping through the script, but then I land up in an "anonymous function" - which is where I hit the limits of my current understanding of this problem. I've tried moving the scrollEnded() function to the top. I've tried all sorts of things...

What can I do to make this work? (Can this thing work?)

Please don't pass strings to `setTimeout` and `setInterval`. It's `eval` in disguise, and every time you `eval`, a ninja kills a cute baby animal. — Matt Ball, Apr 01 '11 at 15:38

score 1 · Answer 1 · answered Nov 15 '12 at 13:25

As an addition to all this answers I would only suggest setting 200ms timeout instead of 500. 200ms is the average human eye reaction between finger move and the eyes expecting to see the effect. 200ms timeout should be short enough to not be noticed by user and long enough for javascript to fire and finish the event. I've tried 200ms before and it seems to work just fine, even on slower PC's.

score 0 · Answer 2 · answered Apr 01 '11 at 15:38

have you tried putting scrollEnded() on top of bodyScroll()?

function scrollEnded(){
    console.log('scrollEnded. Now do something astounding.');
};
function bodyScroll() {
    console.log('scrolling.');

    if (scrollTimer != -1)
        clearTimeout(scrollTimer);

    scrollTimer = window.setTimeout('scrollEnded()', 500);

};

score 0 · Accepted Answer · answered Apr 01 '11 at 15:42

0

The jQuery throttle/debounce plugin is perfect for this. Use at_begin = false to execute the callback at the end.

var scrollEnded = $.debounce(500, false, function ()
{
    console.log('scroll ended');
});

$('#scrollableDiv').scroll(scrollEnded);

Demo

answered Apr 01 '11 at 15:42

Matt Ball

354,903
100
647
710

@ Matt. This works exactly the way I want it to. Perfect. Thanks. – Apr 03 '11 at 07:29

whoughton · Answer 4 · 2011-04-01T15:43:51.273

-1

Sorry, I completely ignored the fact that the function was within the closure, and therefore not available to the page in my earlier response. You could make it work via something like:

window.scrollEnded = function () { console.log('scrollEnded. No do something astounding'); }

followed by a

window.setTimeout(window.scrollEnded, 500);

That should remove the eval of the string, as well as put it in a global scope to where it is available. There are other oddities about that in terms of namespace pollution, but for the time being I'm trying to be somewhat simple and help you get it work.

edited Apr 01 '11 at 15:43

answered Apr 01 '11 at 15:37

whoughton

1,395
11
21

1

Avoid using strings in setTimeout, this uses eval which is considered bad practice. Instead use an anonymous function such as: scrollTimer = setTimeout(function(){ scrollEnded(); }, 500); – JaredMcAteer Apr 01 '11 at 15:38
I tried this and it works...why the "-1"? Was that for the solution before it was edited? – Apr 03 '11 at 06:18
The initial setup had scrollEnded in quotes, which forces an eval call which you generally want to stay away from. Really just an artifact of trying to answer quickly. – whoughton Apr 03 '11 at 18:29

How to call a function after scroll has ended?

4 Answers4

Linked