Fire JavaScript Event When a DIV is in View - javascript

Is it possible to fire a specific JavaScript event when a certain DIV comes into view on the page?
Say, for example, I have a very large page, like 2500x2500 and I have a 40x40 div that sits at position 1980x1250. The div is not necessarily manually positioned, it could be there due to the content pushing it there. Now, is it possible to run a function when the user scrolls to a point where the div becomes visible?

Not automatically. You would have to catch scroll events and check for it being in view each time by comparing the co-ordinates of the div rectangle with the visible page rectangle.
Here's a minimal example.
<div id="importantdiv">hello</div>
<script type="text/javascript">
function VisibilityMonitor(element, showfn, hidefn) {
var isshown= false;
function check() {
if (rectsIntersect(getPageRect(), getElementRect(element)) !== isshown) {
isshown= !isshown;
isshown? showfn() : hidefn();
}
};
window.onscroll=window.onresize= check;
check();
}
function getPageRect() {
var isquirks= document.compatMode!=='BackCompat';
var page= isquirks? document.documentElement : document.body;
var x= page.scrollLeft;
var y= page.scrollTop;
var w= 'innerWidth' in window? window.innerWidth : page.clientWidth;
var h= 'innerHeight' in window? window.innerHeight : page.clientHeight;
return [x, y, x+w, y+h];
}
function getElementRect(element) {
var x= 0, y= 0;
var w= element.offsetWidth, h= element.offsetHeight;
while (element.offsetParent!==null) {
x+= element.offsetLeft;
y+= element.offsetTop;
element= element.offsetParent;
}
return [x, y, x+w, y+h];
}
function rectsIntersect(a, b) {
return a[0]<b[2] && a[2]>b[0] && a[1]<b[3] && a[3]>b[1];
}
VisibilityMonitor(
document.getElementById('importantdiv'),
function() {
alert('div in view!');
},
function() {
alert('div gone away!');
}
);
</script>
You could improve this by:
making it catch onscroll on all ancestors that have overflow scroll or auto and adjusting the top/left co-ords for their scroll positions
detecting overflow scroll, auto and hidden cropping putting the div off-screen
using addEventListener/attachEvent to allow multiple VisibilityMonitors and other things using the resize/scroll events
some compatibility hacks to getElementRect to make the co-ords more accurate in some cases, and some event unbinding to avoid IE6-7 memory leaks, if you really need to.

Here is a solution that is ideal in 2022. The current top answer only allows you to observe one item, and has performance issues because it fires many times every time the page scrolls.
var observer = new IntersectionObserver(function(entries) {
if(entries[0].isIntersecting === true) {
console.log('Item has just APPEARED!');
} else {
console.log('Item has just DISAPPEARED!');
}
}, { threshold: [0] });
observer.observe(document.querySelector("#DIV-TO-OBSERVE"));
This fires as soon as the item is partially on screen. Changing threshold to 1 will require the item to be fully on screen (so it will never fire if the item is bigger than the viewport). You can do values in between for example 0.25 to fire when at least 1/4 of the item is in view.

Here's an starter example using jQuery:
<html>
<head><title>In View</title></head>
<body>
<div style="text-align:center; font-size:larger" id="top"></div>
<fieldset style="text-align:center; font-size:larger" id="middle">
<legend id="msg"></legend>
<div> </div>
<div id="findme">Here I am!!!</div>
</fieldset>
<div style="text-align:center; font-size:larger" id="bottom"></div>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.1/jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
var $findme = $('#findme'),
$msg = $('#msg');
function Scrolled() {
var findmeOffset = $findme.offset(),
findmeTop = findmeOffset.top,
scrollTop = $(document).scrollTop(),
visibleBottom = window.innerHeight;
if (findmeTop < scrollTop + visibleBottom) {
$msg.text('findme is visible');
}
else {
$msg.text('findme is NOT visible');
}
}
function Setup() {
var $top = $('#top'),
$bottom = $('#bottom');
$top.height(500);
$bottom.height(500);
$(window).scroll(function() {
Scrolled();
});
}
$(document).ready(function() {
Setup();
});
</script>
</body>
</html>
It only notifies once the div comes into view from the bottom. This example does not notify when the div scrolls out of the top.

Related

How to prevent hard jumping and what is alternative to position: sticky?

Two questions:
Focus on the part of 'Get early access' bar. It is positioned with position:relative and I want to have it sticky once you move to the 2nd section. I've tried to add helper with the same height in order to get smooth transition when I change the .class to fixed. But not working.
This with helper in previous websites helped me but now it doesn't work and it really bothers me.
What would be alternative to position sticky which works in all browsers? In this particular case, how needs jquery to look like?
Thanks in advance.
/**
* Zirelco
* Custom JS functions
*/
jQuery(document).ready(function ( $ ) {
var mn = $("#sticky-wrapper");
mns = "nav--scrolled";
hdr = $("#top-wrapper-v1").height();
$(window).scroll(function() {
if( $(this).scrollTop() > hdr ) {
mn.addClass(mns);
} else {
mn.removeClass(mns);
}
});
$('.cookies .btn').on('click', function() {
if ($('.cookies').css('opacity') == 0) {
$('.cookies').css('opacity', 1);
}
else {
$('.cookies').addClass('none');
}
});
});
Edit V3
Try this Code instead of yours:
(function(selector) {
selector = selector || '#sticky-wrapper';
var stickyWrapper = document.querySelector(selector)
var stickyTrigger = document.createElement('div')
stickyTrigger.classList.add('sticky-trigger')
stickyWrapper.parentElement.insertBefore(stickyTrigger, stickyWrapper)
var listener = function (e) {
if (stickyTrigger.getBoundingClientRect().top < 0) {
stickyWrapper.classList.add('sticky');
} else {
stickyWrapper.classList.remove('sticky');
}
}
var onScroll = document.addEventListener('scroll', listener);
}('#sticky-wrapper'))
What this does is:
create a .sticky-trigger element
insert this right before #sticky-wrapper
watch for scroll event of document
check the top property of getBoundingClientRect of the .sticky-trigger element
toggle the sticky class of #sticky-wrapper depending on the sign (positive or negative) of that top value
You don't have to change your HTML output at all
Old V1
You use the height of the #top-wrapper-v1 <section> as trigger for the class toggle. But you totally forget the to calc the <header> height as well.
To prevent such mistakes just go for the top edge of the '#sticky-wrapper' as a trigger
// $(window).scroll(function(e) {
// if( $(this).scrollTop() > mn.offset().top ) {
// mn.addClass('sticky');
// } else {
// mn.removeClass('sticky');
// }
//});
Old V2
Because of the comment of the asker, this is an improved way of doing it.
In the previous example, the measurement of the offset().top of #sticky-wrapper is immediately set to 0 caused by position: fixed. In order to break this issue, we wrap the #sticky-wrapper in a trigger element, measure the offset().top of that element as trigger. This trigger element will remain in the document flow and will not be fixed
HTML
<!--
<section id="sticky-trigger">
<section id="sticky-wrapper" class="">
<div class="container" style="position: fixed;top: 0;">
Other content
</div>
</section>
</section>
-->
JavaScript
// var trigger = document.querySelector('#sticky-trigger')
// $(window).scroll(function(e) {
//
// if( $(this).scrollTop() > trigger.offset().top ) {
// mn.addClass('sticky');
// } else {
// mn.removeClass('sticky');
// }
// });

How do I code JQuery so that when I scroll to a certain element, Nav bar appears at top, when I scroll back up past that element, nav bar disappears

I have a div called #menu which I want to display when I scroll past the element #section3, if I scroll up past that element again, I want #menu to disappear
How would I code this?
Maybe something like this?
scrolled = "no"
$(window).scroll(function(){
scr = $("body").scrollTop();
if (scr > 100 && scrolled == "no"){
$("#menu").css({"display:block"})
displayed = "yes"
}
if (displayed == "yes" && scrolled = "yes"){
$("#menu").css({"display:none"})
}
});
The above assumes that #section3 is 100 pixels down the page. If you do not know where its going to be on the page then you could use the method outlined here:
Trigger event when user scroll to specific element - with jQuery
With jQuery you can get the scroll position with $("body").scrollTop();.
Expanding on what #Ned Hulton said, I recommend comparing the scroll position to the top of a "container element" (or 'row') in your page like this:
if ($('body').scrollTop() > $('#someRow').offset().top){
//do something
}
That way you can account for your container appearing at a variable distance down the page (which will come in handy for mobile browsing or cases where your text wraps to additional lines)
I just whipped this up in jsfiddle
https://jsfiddle.net/rb56j0yu/
it uses jQuery, and checks the scroll position against the target div. Css sets the menu as position: fixed, and defaults to hidden.
$(window).scroll(function(){
var yPos = $("body").scrollTop();
var yCheck = $("#c3").position().top;
if (yPos > yCheck && !$("#menu").is(":visible"))
{
$("#menu").show();
}
if (yPos <= yCheck && $("#menu").is(":visible"))
{
$("#menu").hide();
}
});
First, get your #section3 top offset and height. Which will be used as the threshold whether #section3 is actually on the window screen.
var top = $('#section3').offset().top;
var bot = topOffset + $('#section3').height();
Then, detect it on your scroll event.
$(window).on('scroll', function () {
var scrollTop = $(window).scrollTop();
if (scrollTop >= top && scrollTop <= bot) {
// #section3 is within the screen.
$('#menu').show();
}
else {
// #section3 is out of screen.
$('#menu').hide();
}
});
This is a common use case, I wrote following code:
// what does "Auto Header" mean, goto https://www.yahoo.com/
// scroll down and you will see the purple part auto fixed to top,
// while when scroll up, it restores and does not be fixed.
// 1. multiple auto header elements handled
// 2. dynamically create/remove elements issue handled
// 3. no unnecessary dom operation, high performance
// usage: just add 'class="auto-header"' to any element you want to auto header
// suggest set each auto-header element specific width and height
// do not guarantee it works when resize or scroll left/right
$(document).ready(function() {
var rawTops = [],
rawLefts = [],
rawStyles = [],
$locations = [], // record next sibling so that element easily find where to restore
fixed = []; // mark whether this element is fixed
$(".auto-header").each(function() {
var $this = $(this),
offset = $this.offset();
rawTops.push(offset.top);
rawLefts.push(offset.left);
rawStyles.push($this.attr("style"));
$locations.push($this.siblings().eq($this.index()));
fixed.push(false);
});
$(window).on("scroll", function() {
$(".auto-header").each(function(i, e) {
if(!fixed[i] && $(window).scrollTop() > rawTops[i]) {
var $te = $(this).clone(true);
$(this).remove();
$locations[i].before($te);
$te.css({
"position": "fixed",
"top": 0,
"left": rawLefts[i],
"z-index": 100
});
fixed[i] = true;
} else if(fixed[i] && $(window).scrollTop() < rawTops[i]) {
$(this).removeAttr("style").attr("style", rawStyles[i]);
fixed[i] = false;
}
});
});
});

How can I set my browser window's scrollbar or a div scrollbar to scroll in increments using animate and scrollTop?

The general idea to the site i am designing is to scroll through a set of menu items horizontally and incrementally underneath a static div that will magnify(increase dimensions and pt size) the contents of a menu items. I don't really need help with the magnify portion because i think it's as simple as adding a mag class to any of the menuItem divs that go underneath the static div. I have been messing with this for a few weeks and the code I have for incrementally scrolling, so far, is this:
$(document).ready(function () {
currentScrollPos = $('#scrollableDiv').scrollTop(120); //sets default scroll pos
/*The incrementScroll function is passed arguments currentScrollPos and UserScroll which are variables that i have initiated earlier in the program, and then initiates a for loop.
-The first statement sets up the variables: nextScrollPos as equal to the currentScrollPos(which by default is 120px) plus 240px(the distance to next menuItem), prevScrollPos as equal to the currentScrollPos(which by default is 120px) minus 240px(the distance to next menuItem).
-The second Statement checks to see if the user has scrolled using var userScroll
-The third statement sets: var CurrentScroll equal to the new scroll position and var userScroll to false*/
function incrementScroll(currentScrollPos, userScroll) {
for (var nextScrollPos = parseInt(currentScrollPos + 240, 10),
prevScrollPos = parseInt(currentScrollPos - 240, 10); //end first statement
userScroll == 'true'; console.log('dude'), //end second statement and begining of third
currentScrollPos = scrollTop(), userScroll = 'false') {
if (scrollTop() < currentScrollPos) {
$('#scrollableDiv').animate({
scrollTop: (parseInt(prevScrollPos, 10))
}, 200);
console.log('scrolln up')
} else if (scrollTop() > currentScrollPos) {
$('#scrollableDiv').animate({
scrollTop: (parseInt(nextScrollPos, 10))
}, 200);
console.log('scrolln down')//fire when
}
}
}
$('#scrollableDiv').scroll(function () {
userScroll = 'true';
_.debounce(incrementScroll, 200); //controls the amount of times the incrementScroll function is called
console.log('straight scrolln')
});
});
I have found a variety of solutions that are nigh close: such as a plugin that snaps to the next or previous div horizontally demo, another solution that also snaps and is based on setTimeout demo, but nothing that nails incrementally scrolling through divs. I also found a way to control the rate at which a user may scroll through the menuItems using debounce which is included in the above code.
The console.logs inside the loop do not fire when I demo the code in jsfiddle which leads me to believe the problem lies within the loop. I'm a noob though so it could be in syntax or anywhere else in the code for that matter. Also in the second demo, i have provided the css for the horizontal static div, but the moment I put it in my html it keeps the js from working.
I would like to write the code instead of using a plugin and any help would be appreciated! Also, thank you ahead of time!
Try this fiddle. Menu container height is 960px to show 4 menu items. "Zoom" div is positioned absolutely at top. When you scroll mouse over this div, menu items shifts to top/bottom. I had to add additional div to bottom to be able to scroll to last 3 menu items. JS code:
jQuery(document).ready(function($){
var current = 0;
var menu = $('.menu-container').scrollTop(0);
var items = menu.find('.menu-item');
var zoom = $('.zoom');
function isVerticalScroll(event){
var e = event.originalEvent;
if (e.axis && e.axis === e.HORIZONTAL_AXIS)
return false;
if (e.wheelDeltaX)
return false;
return true;
}
function handleMouseScroll(event){
if(isVerticalScroll(event)){
var delta = event.originalEvent.wheelDelta * -1 || event.originalEvent.detail;
current += (delta > 0 ? 1 : -1);
if(current < 0)
current = 0;
if(current >= items.length){
current = items.length - 1;
}
menu.stop().animate({
"scrollTop": current * 240
}, 300);
items.removeClass('current').eq(current).addClass('current');
event && event.preventDefault();
return false;
}
}
zoom.on({
"MozMousePixelScroll": handleMouseScroll,
"mousewheel": handleMouseScroll
});
});
Hope it will help.

jQuery infinite scrolling scrolling in fixed div

Background
I am trying to create an infinite scrolling table inside a fixed position div. The problem is that all the solutions I come across use the window height and document scrollTop to calculate if the user has scrolled to the bottom of the screen.
Problem
I have tried to create a jQuery plugin that can calculate if a user has scrolled to the bottom of a fixed div with overflow: scroll; set.
My approach has been to create a wrapper div (the div with a fixed position and overflow: scroll) that wraps the table, I also place another div at the bottom of the table. I then try calculate if the wrapper.scrollTop() is greater than the bottom div position.top every time the wrapper is scrolled. I then load the new records and append them to the table body.
$.fn.isScrolledTo = function () {
var element = $(this);
var bottom = element.find('.bottom');
$(element).scroll(function () {
if (element.scrollTop() >= bottom.position().top) {
var tableBody = element.find("tbody");
tableBody.append(tableBody.html());
}
});
};
$('.fixed').isScrolledTo();
See Example http://jsfiddle.net/leviputna/v4q3a/
Question
Clearly my current example is not correct. My question is how to I detect when a user has scrolled to the bottom of a fixed div with overflow:scroll set?
Using the bottom element is a bit clunky, I think. Instead, why not use the scrollHeight and height to test once the scrollable area has run out.
$.fn.isScrolledTo = function () {
var element = this,
tableBody = this.find("tbody");
element.scroll(function(){
if( element.scrollTop() >= element[0].scrollHeight-element.height()){
tableBody.append(tableBody.html());
}
});
};
$('.fixed').isScrolledTo();
EDIT (12/30/14):
A DRYer version of the plugin might be much more re-usable:
$.fn.whenScrolledToBottom = function (cback_fxn) {
this.on('scroll',this,function(){
if( ev.data.scrollTop() >= ev.data[0].scrollHeight - ev.data.height()){
return cback_fxn.apply(ev.data, arguments)
}
});
};
Plugin Usage:
var $fixed = $('.fixed'),
$tableBody = $fixed.find("tbody");
$fixed.whenScrolledToBottom(function(){
// Load more data..
$tableBody.append($tableBody.html());
});
I have modified your code to handle the scroll event with a timer threshold:
$.fn.isScrolledTo = function () {
var element = $(this);
var bottom = element.find('.bottom');
$(element).scroll(function(){
if (this.timer) clearTimeout(this.timer);
this.timer=setTimeout(function(){
if( element.scrollTop() >= bottom.position().top){
var tableBody = element.find("tbody");
tableBody.append(tableBody.html());
}
},300);
});
};
$('.fixed').isScrolledTo();
The issue you are having is that as you scroll, new scroll event is being generated. Your code might have other issues, but this is a start.

Change z-index after load

I have a function that gets called when a user scrolls to check for scrollTop() and after a certain scroll happens it changes the menu's z-index from -1 to 1. However this only occurs on a scroll so if the user refreshes the site the menu is virtually unusable until the next scroll occurs.
Is there a way for me to call this and check if the amount of screen scrolled (after the refresh not a user scroll) meets the criteria change the z-index?
My JS:
function getPosition(){
var y = $(window).scrollTop();
var status = (y > 880) ? true : false;
//console.log(status);
if(status)
$('#actual-menu').css('z-index', 1);
else
$('#actual-menu').css('z-index', -1);
}
z-index property has no effect on non-positioned elements, the element must be either relatively positioned ,absolutely positioned, or fixed.Replace your line with this:
Try adding this first ,
$("#actual-menu").css('position', 'relative');
$('#actual-menu').css('z-index', 1);
Just run getPosition inside of your ready event.
Functioning Example
var limit = 50;
$(function () {
function getPosition() {
var y = $(window).scrollTop();
var status = (y > limit) ? true : false;
if (status) {
$('#actual-menu').css('zIndex', 1);
} else {
$('#actual-menu').css('zIndex', -1);
}
}
$(document).on('scroll', getPosition);
getPosition();
});

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