Igor's Blog

I've recently discovered that on Mobile Safari the $(window).scrollTop() would not update during the scroll event animation. It appeared to only update after the scroll (the elastic scroll) had finished its animation. This was a rather annoying 'feature' for me because I needed to update my UI during the animation, so I went looking for a workaround and here's what I've come up with.

Below are two videos showing the before and after the workaround. The first video shows the default behaviour where scrollTop() is only updated after the scroll event completes, the second video shows a workaround that has continuous updates during scrolling.



This was my 'before' code:
 Before Code
<!DOCTYPE html>
<html lang="en">
<head>
<title>ScrollTop test</title>
<script src="https://code.jquery.com/jquery-2.2.4.min.js"></script>
<style>
div#message {
position: fixed;
right: 0;
top: 0;
color: red;
font-size: 300%;
}
</style>
</head>
<body>
<div id="body">
<div id="message"></div>
</div>
<div id="content" style="display: none; margin: 1em;"></div>
<script>
$(document).ready(function() {
/* generate some content */
for (var i = 0; i < 100; i++) {
$('#content').clone().text('Content item ' + i).show().appendTo($('#body'));
}
$(document).scroll(function(e) {
var scrollTop = $(window).scrollTop();
$('#message').text('Scroll Top: ' + scrollTop);
});
});
</script>
</body>
</html>




The main part of the code was the $(document).scroll() event handler. There the $(window).scrollTop() is looked up and set as text for display. Nothing fancy. That was the code for the first video.

My workaround to make continuous scrolling work added a couple of modifications...

First I set my div#body style so that it stretched to the size of the viewport, like so:
 CSS
div#body {
position: absolute;
top: 0;
bottom: 0;
left: 0;
right: 0;
overflow-y: scroll;
-webkit-overflow-scrolling: touch;
}


The second modification was to change the $(document).scroll() to this code:
 JavaScript
$('#body').scroll(function(e) {
var scrollTop = $(e.target).scrollTop();
$('#message').text('Scroll Top: ' + scrollTop);
});


The workaround responds to scroll events on the div#body instead and looks up scrollTop() on that DIV element instead of on the window object. This way continuous scroll events can be detected. The modified code was used in the second video.

You can get the source code for the before and after code on my GitHub - before code and after code.

-i

comments powered by Disqus
Other posts you may like...
Programming, DIY, Games, Hacks, and Tech

Recent Blog Posts

Converting a CSV file containing commas in quotes to a pipe separated file using Awk and Bash

How to get Facybox gallery popup to work for images with dynamic URLs

jQuery UI Photoboxr plugin updated to version 0.2

Learn How to Add Disclaimer to All Outgoing Emails in Office 365

How to securely host your web site for free with Google Cloud and CloudFlare (part 3)

How to securely host your web site for free with Google Cloud and CloudFlare (part 2)

How to securely host your web site for free with Google Cloud and CloudFlare (part 1)

Beware of the subtle difference in date format strings between MySQL and SQLite

Postman reporting Unexpected 'N' error in response body

Adding extra shelves to the Ikea Detolf display cabinet

Recent Galleries

Space Food - Chocolate Ice Cream with Chocolate Chips

Legeod Star Wars AT-DP kit

DIY spare parts computer build with a RAIDMAX Anura case

Fake 'Lepin' brand Lego packaging

Hardwood garden bench with clear resin void filler

Fixing a 3D printer extruder that stopped heating up

Easily increase disk space in a Lenovo Ideapad 100S 14" laptop with an M.2 SSD

Making a multi-piece 3D printed solder spool holder stand

DIY indoor apartment grow light wiring

Good Friday Electronics fun Easter Bunny LED PCB Kit IBEABU-01.0

My Other Web Sites

Igor and Elise's Travels
Riverside Expressway Cam
300 George St Blogumentary

My Online Tools

UUID to OID Converter
Guru JSON-RPC Tester
Extrudifier Object Designer
Travel ┬ÁBlog

Blogs and Friends

Matt Moores Blog
Georgi's FlatPress Guide
Perplexing Permutations
The Security Sleuth
Ilia Rogatchevski
Travelling Fairy

Blog Activity

Blog Activity
Please follow me for more great content!
     
Don't show this again