Develop Reference

jQuery "Snap To" Effect

I have a specific effect I want for a website I'm building. As you can see in this website, I want the screen to "snap to" the next section after the user scrolls, but only after (not the instant) the scroll event has fired. The reason I don't want to use a plugin like panelSnap is because I
1: Want smaller code and
2. Want the website, when viewed on mobile, to have more of the "instant snap" effect (try reducing the browser size in the website mentioned above). I know I theoretically could try combining two plugins, like panelsnap and scrollify, and activate them appropriately when the browser is a certain width, but I don't know if I want to do that... :(
So all of that said, here's the code:
var scrollTimeout = null;
var currentElem = 0;
var options = {
scrollSpeed: 1100,
selector: 'div.panels',
scrollDelay: 500,
};
$(document).ready(function() {
var $snapElems = $(options.selector);
console.log($($snapElems[currentElem]).offset().top);
function snap() {
if ($('html, body').scrollTop() >= $($snapElems[currentElem]).offset().top) {
if (currentElem < $snapElems.length-1) {
currentElem++;
}
}else{
if (currentElem > 0) {
currentElem = currentElem - 1;
}
}
$('html, body').animate({
scrollTop: $($snapElems[currentElem]).offset().top
}, options.scrollSpeed);
}
$(window).scroll(function() {
if ($(window).innerWidth() > 766) {
if (scrollTimeout) {clearTimeout(scrollTimeout);}
scrollTimeout = setTimeout(function(){snap()}, options.scrollDelay);
}else{
//I'll deal with this later
}
});
});
My problem is that every time the snap function is called, it triggers the scroll event, which throws it into a loop where the window won't stop scrolling between the first and second elements. Here's the poor, dysfunctional site: https://tcfchurch.herokuapp.com/index.html Thank for the help.

You can use a boolean to record when the scroll animation in snap is in progress and prevent your $(window).scroll() event handler from taking any action.
Here's a working example:
var scrollTimeout = null;
var currentElem = 0;
var options = {
scrollSpeed: 1100,
selector: 'div.panels',
scrollDelay: 500,
};
$(document).ready(function() {
var scrollInProgress = false;
var $snapElems = $(options.selector);
console.log($($snapElems[currentElem]).offset().top);
function snap() {
if ($('html, body').scrollTop() >= $($snapElems[currentElem]).offset().top) {
if (currentElem < $snapElems.length-1) {
currentElem++;
}
}else{
if (currentElem > 0) {
currentElem = currentElem - 1;
}
}
scrollInProgress = true;
$('html, body').animate({
scrollTop: $($snapElems[currentElem]).offset().top
}, options.scrollSpeed, 'swing', function() {
// this function is invoked when the scroll animate is complete
scrollInProgress = false;
});
}
$(window).scroll(function() {
if (scrollInProgress == false) {
if ($(window).innerWidth() > 766) {
if (scrollTimeout) {clearTimeout(scrollTimeout);}
scrollTimeout = setTimeout(function(){snap()}, options.scrollDelay);
}else{
//I'll deal with this later
}
}
});
});
The variable scrollInProgress is set to false by default. It is then set to true when the scroll animate starts. When the animate finishes, scrollInProgress is set back to false. A simple if statement at the top of your $(window).scroll() event handler prevents the handler from taking any action while the animate scroll is in progress.

Have you considered using the well known fullPage.js library for that? Check out this normal scroll example. The snap timeout is configurable through the option fitToSectionDelay.
And nothing to worry about the size... it is 7Kb Gzipped!
I know I theoretically could try combining two plugins, like panelsnap and scrollify, and activate them appropriately when the browser is a certain width, but I don't know if I want to do that
fullPage.js also provides responsiveWidth and responsiveHeight options to turn it off under certain dimensions.

Too many scroll events for smooth scrolling

Hello there I've been trying to find a fix for the many scroll events firing on one scroll. This is the only thing close to working for me so far. I want to smoothscroll between two divs (#boxes and #header) I want to use the scroll bar to trigger this smooth scroll and not a button. Any suggestions on how to only take one scroll event? I also used solutions based from prev stackoverflow questions. I used my own locator instead of offsets because thats also unreliable
$(window).scroll(function () {
if (timer) {
window.clearTimeout(timer);
}
timer = window.setTimeout(function () {
if (locator == 0) {
id = $("#boxes");
locator = 1;
} else if (locator = 1) {
id = $("#header");
locator = 0;
}
// target element
var $id = $(id);
if ($id.length === 0) {
return;
}
// top position relative to the document
var pos = $id.offset().top;
// animated top scrolling
$('html, body').animate({scrollTop: pos}, 1500, function () {
$('html, body').clearQueue();
$('html, body').stop();
});
}, 2);
});

So, to be clear, you want any minor scroll event to scroll between one item and the other? Note that when a user scrolls, there is a "momentum" that the browser implements, and you'll be battling with that.
Regardless: You don't need to wrap this in a setTimeout. Right now, your javascript is creating a new setTimeout function that is being fired every 2ms. Scroll events occur with every pixel of movement in the scroll, so if you scroll 100px, you're going to be firing 100 times every 2ms. (That's 50,000 times).
Instead, have a a variable (isScrolling) track the state, so, if you're in the middle of scrolling, the function won't fire.
var isScrolling = false;
var locator = 0;
$(window).scroll(function () {
if (isScrolling) return false;
if (locator == 0) {
id = $("#boxes");
locator = 1;
} else if (locator = 1) {
id = $("#header");
locator = 0;
}
// target element
var $id = $(id);
if ($id.length === 0) {
return;
}
// top position relative to the document
var pos = $id.offset().top;
// animated top scrolling
isScrolling = true;
$('html, body').animate({scrollTop: pos}, 1500, function () {
$('html, body').clearQueue();
$('html, body').stop();
isScrolling = false;
});
});
Here's a JSbin: http://jsbin.com/jugefup/edit?html,css,js,output

Slide div on and off the page on scroll without interrupting the animation when the user continues to scroll

I am trying to smoothly slide a div on and off the page (left to right) using jQuery only. I have accomplished the task, however if you continue to scroll up or down while the animation is still going, it will interrupt it in the middle of the action causing it to hesitate. I've run into this issue before and could never figure it out without using a plugin of some sort.
I know how to accomplish this with CSS transitions, jQuery UI, greensock, etc., but I am curious if there is a way to prevent that interruption with jQuery only. I am open to a pure JavaScript solution (no jQuery) as well if there is one.
My code:
var amountScrolled = 50;
$(window).scroll(function() {
if ($(window).scrollTop() > amountScrolled) {
$('#slide').stop().animate({marginLeft:"0px"}, 500);
} else {
$('#slide').stop().animate({marginLeft: "-400px"}, 500);
}
});
Example: https://jsfiddle.net/Hysteresis/hg9cvxop/6/

This works: JSFIDDLE link
It's all about the Callback Functions!
var amountScrolled = 50;
var loopRunning = 0;
$(window).scroll(function() {
if ($(window).scrollTop() > amountScrolled){
if(loopRunning === 0){
animateSlide("0px",500);
}
} else {
if(loopRunning === 0){
animateSlide("-400px",500);
}
}
});
function animateSlide(px, time){
loopRunning = 1;
$('#slide').stop().animate({marginLeft:px}, time, function(){
loopRunning = 0;
});
}

Well, to answer your question rather than provide advice on better ways to do it, I usually handle tasks like this by assigning a temporary class to denote that something is in the process of being animated. As somebody else said, the reason for the stuttering is because the scroll function is getting called multiple times, so you keep stopping and restarting the animation.
So you can try something like this (Fiddle):
var amountScrolled = 50;
$(window).scroll(function() {
if ($('#slide').hasClass('sliding')) {
return;
}
if ($(window).scrollTop() > amountScrolled) {
$('#slide').stop().addClass('sliding').animate({marginLeft:"0px"}, 500, function() {
$(this).removeClass('sliding');
});
} else {
$('#slide').stop().addClass('sliding').animate({marginLeft: "-400px"}, 500, function() {
$(this).removeClass('sliding');
});
}
});

Adding listener for position on screen

I'd like to set something up on my site where when you scroll within 15% of the bottom of the page an element flyouts from the side... I'm not sure how to get started here... should I add a listener for a scroll function or something?
I'm trying to recreate the effect at the bottom of this page: http://www.nytimes.com/2011/01/25/world/europe/25moscow.html?_r=1
update
I have this code....
console.log(document.body.scrollTop); //shows 0
console.log(document.body.scrollHeight * 0.85); //shows 1038.7
if (document.body.scrollTop > document.body.scrollHeight * 0.85) {
console.log();
$('#flyout').animate({
right: '0'
},
5000,
function() {
});
}
the console.log() values aren't changing when I scroll to the bottom of the page. The page is twice as long as my viewport.

[Working Demo]
$(document).ready(function () {
var ROOT = (function () {
var html = document.documentElement;
var htmlScrollTop = html.scrollTop++;
var root = html.scrollTop == htmlScrollTop + 1 ? html : document.body;
html.scrollTop = htmlScrollTop;
return root;
})();
// may be recalculated on resize
var limit = (document.body.scrollHeight - $(window).height()) * 0.85;
var visible = false;
var last = +new Date;
$(window).scroll(function () {
if (+new Date - last > 30) { // more than 30 ms elapsed
if (visible && ROOT.scrollTop < limit) {
setTimeout(function () { hide(); visible = false; }, 1);
} else if (!visible && ROOT.scrollTop > limit) {
setTimeout(function () { show(); visible = true; }, 1);
}
last = +new Date;
}
});
});

I know this is an old topic, but the above code that received the check mark was also triggering the $(window).scroll() event listener too many times.
I guess twitter had this same issue at one point. John Resig blogged about it here: http://ejohn.org/blog/learning-from-twitter/
$(document).ready(function(){
var ROOT = (function () {
var html = document.documentElement;
var htmlScrollTop = html.scrollTop++;
var root = html.scrollTop == htmlScrollTop + 1 ? html : document.body;
html.scrollTop = htmlScrollTop;
return root;
})();
// may be recalculated on resize
var limit = (document.body.scrollHeight - $(window).height()) * 0.85;
var visible = false;
var last = +new Date;
var didScroll = false;
$(window).scroll(function(){
didScroll = true;
})
setInterval(function(){
if(didScroll){
didScroll = false;
if (visible && ROOT.scrollTop < limit) {
hideCredit();
visible = false;
} else if (!visible && ROOT.scrollTop > limit) {
showCredit();
visible = true;
}
}
}, 30);
function hideCredit(){
console.log('The hideCredit function has been called.');
}
function showCredit(){
console.log('The showCredit function has been called.');
}
});
So the difference between the two blocks of code is when and how the timer is called. In this code the timer is called off the bat. So every 30 millaseconds, it checks to see if the page has been scrolled. if it's been scrolled, then it checks to see if we've passed the point on the page where we want to show the hidden content. Then, if that checks true, the actual function then gets called to show the content. (In my case I've just got a console.log print out in there right now.
This seems to be better to me than the other solution because the final function only gets called once per iteration. With the other solution, the final function was being called between 4 and 5 times. That's got to be saving resources. But maybe I'm missing something.

bad idea to capture the scroll event, best to use a timer and every few milliseconds check the scroll position and if in the range you need then execute the necessary code for what you need
Update: in the past few years the best practice is to subscribe to the event and use a throttle avoiding excessive processing https://lodash.com/docs#throttle

Something like this should work:
$(window).scroll(function() {
if (document.body.scrollTop > document.body.scrollHeight * 0.85) {
// flyout
}
});
document.body.scrollTop may not work equally well on all browsers (it actually depends on browser and doctype); so we need to abstract that in a function.
Also, we need to flyout only one time. So we can unbind the event handler after having flyed out.
And we don't want the flyout effect to slow down scrolling, so we will run our flytout function out of the event loop (by using setTimeout()).
Here is the final code:
// we bind the scroll event, with the 'flyout' namespace
// so we can unbind easily
$(window).bind('scroll.flyout', (function() {
// this function is defined only once
// it is private to our event handler
function getScrollTop() {
// if one of these values evaluates to false, this picks the other
return (document.documentElement.scrollTop||document.body.scrollTop);
}
// this is the actual event handler
// it has the getScrollTop() in its scope
return function() {
if (getScrollTop() > (document.body.scrollHeight-$(window).height()) * 0.85) {
// flyout
// out of the event loop
setTimeout(function() {
alert('flyout!');
}, 1);
// unbind the event handler
// so that it's not call anymore
$(this).unbind('scroll.flyout');
}
};
})());
So in the end, only getScrollTop() > document.body.scrollHeight * 0.85 is executed at each scroll event, which is acceptable.
The flyout effect is ran only one time, and after the event has returned, so it won't affect scrolling.

Resetting a function, or perhaps stopping something and starting it again?

I have this code:
$(document).ready(function() {
var number = 10;
var offset = 10;
var page_number = 2;
/* Bind the scroll function to an event */
$(window).bind('scroll', function(e) {
/* If the scroll height plus the window height is
more than the document height minus 10, continue */
if($(window).scrollTop() + $(window).height() >
$(document).height() - 10) {
/* Quick message so you know more stuff is loading */
$('.loading-more').html('Keep scrolling for more posts to load..');
$.post('<?php bloginfo('siteurl') ?>/wp-admin/admin-ajax.php', {
action: 'and_action',
off: offset+number,
pagenumber: page_number - 1
}, function(data) {
offset = offset+number;
$('.empty-div').append('<p><strong>Page '+page_number+'</strong></p><br />'+data);
page_number += 1;
$(this).unbind(e);
});
}
});
});
This checks if the user is near the bottom of the page and loads more content. The problem is if the user scrolls slowly near the critical point, or scrolls up and down over and over again really fast, the $.post function runs a few times, meaning you end up with a few instances of the data I'm loading.
What I had tried doing was binding and unbinding the e variable, but it didn't work so good. Is there anyway to perhaps run the post function once, and then have the function reset so when the user scrolls down again it will run again, so more than one instance of the data doesn't load?

Why don't you just set a boolean as a representation of the current state: loading/ready.
$(document).ready(function () {
var busy = false;
$(window).bind('scroll', function (e) {
if( !busy && goodposition){
// load more
busy = true;
$.post(..., function(date){
busy = false;
});
}
});
});

why not do something like this:
var doingWork = false;
if(($(window).scrollTop() + $(window).height() > $(document).height() - 10)
&& !doingWork)
{
doingWork = true;
then reset doingWork to false once you need the functionality back

Two answers have suggested doing this by setting a boolean to note whether a request exists. This is probably the route I'd take. The other option is to cancel the existing request.
$.post returns an XMLHttpRequest object. This means that you can cache the request object and use the .abort() method to cancel an ongoing request:
$(window).bind('scroll', function(e) {
if($(window).scrollTop() + $(window).height() >
$(document).height() - 10) {
$('.loading-more').html('Keep scrolling for more posts to load..');
if (curxhr && (curxhr.readyState != 4) { // if the curxhr object exists and has not completed
curxhr.abort(); // abort the request
}
curxhr = $.post('<?php bloginfo('siteurl') ?>/wp-admin/admin-ajax.php', {
action: 'and_action',
off: offset+number,
pagenumber: page_number - 1
}, function(data) {
// snip
});
}
});