I'm trying to highlight the current section items in a sticky table of contents as you scroll down the page.
The structure is currently like:
<div>
<div>
<div>
<div>
<h2 id="twitter-chats-for-ecommerce">Header</h2>
<div>content...</div>
</div>
</div>
</div>
</div>
And the table of contents like:
<ul>
<li>Item 1</li>
<li>Item 1</li>
<li>Twitter Chats for Ecommerce</li>
</ul>
The anchor is being applied to the header automatically via a Gutenberg block in WordPress (in this case, the h2).
The existing JavaScript for this is the following:
(function($) {
/* Table of contents - highlight active section on scroll */
window.addEventListener('DOMContentLoaded', () => {
const observer = new IntersectionObserver(entries => {
entries.forEach(entry => {
const id = entry.target.getAttribute('id');
if (entry.intersectionRatio > 0) {
document.querySelector(`nav li a[href="#${id}"]`).parentElement.classList.add('active');
} else {
document.querySelector(`nav li a[href="#${id}"]`).parentElement.classList.remove('active');
}
});
});
// Track all sections that have an `id` applied
document.querySelectorAll('h2[id]').forEach((section) => {
observer.observe(section);
});
});
})( jQuery );
But as you can see from the below example screenshot, the item in the table of contents is highlighting when the matching header (in this case h2) is visible on the page.
So in the case where there are multiple headers visible on the page, more than one item is highlighted in the TOC.
Ideally, I guess that it should be matching the div of the section but the id anchor is being applied to the header and I don't have control over this.
Is there a way I can modify the JS to somehow only detect the entire div section instead of just the header so that it will only ever have one item highlighted in the TOC - or is there even a better way than this?
An example of one that works perfectly that I'd like to achieve can be seen here (see the 'On This Page' section in right hand sidebar).
I modified randomdude's answer to highlight the lowest scrolled-to header. This will persist highlighting of that link until the user scrolls down far enough to another one.
const anchors = $('body').find('h1');
$(window).scroll(function(){
var scrollTop = $(document).scrollTop();
// highlight the last scrolled-to: set everything inactive first
for (var i = 0; i < anchors.length; i++){
$('nav ul li a[href="#' + $(anchors[i]).attr('id') + '"]').removeClass('active');
}
// then iterate backwards, on the first match highlight it and break
for (var i = anchors.length-1; i >= 0; i--){
if (scrollTop > $(anchors[i]).offset().top - 75) {
$('nav ul li a[href="#' + $(anchors[i]).attr('id') + '"]').addClass('active');
break;
}
}
});
forked fiddle link: http://jsfiddle.net/tz6yxfk3/
I think you are looking for this:
$(window).scroll(function(){
var scrollTop = $(document).scrollTop();
var anchors = $('body').find('h1');
for (var i = 0; i < anchors.length; i++){
if (scrollTop > $(anchors[i]).offset().top - 50 && scrollTop < $(anchors[i]).offset().top + $(anchors[i]).height() - 50) {
$('nav ul li a[href="#' + $(anchors[i]).attr('id') + '"]').addClass('active');
} else {
$('nav ul li a[href="#' + $(anchors[i]).attr('id') + '"]').removeClass('active');
}
}
});
nav {
position: fixed;
right: 20px;
top: 20px;
}
div {
height: 2000px;
}
div > h1 {
height: 200px;
}
.active {
color: red;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<nav>
<ul>
<li id="whatbutton">What We Are</li>
<li id="whybutton">Why Us</li>
<li id="offerbutton">What We Offer</li>
<li id="contactbutton">Contact Us</li>
</ul>
</nav>
<div>
<h1 id="whatissm" name="whatissm"><span>sometexthere</span></h1>
<h1 id="whyusesm" name="whyusesm"><span>somtexthere</span></h1>
<h1 id="whatdoessmoffer" name="whatdoessmoffer"><span>sometexthere</span></h1>
<h1 id="contactus" name="contactus"><span>Contact Us</span></h1>
</div>
credits: Making a menu class active when scrolled past
fiddle link:
http://jsfiddle.net/yrz54fqm/1/
This is same answer as above, but is written in pure JavaScript, no need for jQuery. Great work, Crane, works like a champ.
const anchors = document.querySelectorAll('h1');
const links = document.querySelectorAll('nav > ul > li > a');
window.addEventListener('scroll', (event) => {
if (typeof(anchors) != 'undefined' && anchors != null && typeof(links) != 'undefined' && links != null) {
let scrollTop = window.scrollY;
// highlight the last scrolled-to: set everything inactive first
links.forEach((link, index) => {
link.classList.remove("active");
});
// then iterate backwards, on the first match highlight it and break
for (var i = anchors.length-1; i >= 0; i--) {
if (scrollTop > anchors[i].offsetTop - 75) {
links[i].classList.add('active');
break;
}
}
}
});
Can someone help me with my code? This code below makes my menu items red on scroll within the div where a "scrollspy" is added. But there is something missing so my first menu item (Home) does not get red when page is loaded, only when I scroll a bit below. I need to have this 1st item red on load. How can I fix this?
An example code to make first menu item active on load?
window.onload = function() {
//code?
};
This makes menu item red when added "scrollspy" class on a row in admin
var elems = $('.scrollspy');
$(window).bind('scroll', function() {
var currentActive = null;
var currentActiveDistance = -1;
var currentTop = $(window).scrollTop();
elems.each(function(index) {
var elemTop = $(this).offset().top - 102
var id = $(this).attr('id');
var navElem = $('.menu a[href="#' + id + '"]');
navElem.removeClass('active');
if (currentTop >= elemTop) {
var distance = currentTop - elemTop;
if (currentActiveDistance > distance || currentActiveDistance == -1) {
currentActive = navElem;
}
}
});
if (currentActive) {
currentActive.addClass('active');
}
});
Why not use just CSS?
.nav li a.active {
background-color: red;
}
jQuery can be used as below to make first menu item link RED i.e by applying class active.
$(document).ready(function(){
$(".menu:first a").addClass('active');
});
Please post your HTML markup if it does not work with your HTML.
I am struggling to get a last bit of my code to work. Problem is I need to fire a function when a user scrolls past a div
So the structure of my html looks roughly like this
<div class="panel-grid-cell">
<div id="pgc-1">...</div>
<div id="pgc-2">...</div>
...
<div id="pgc-n">...</div>
</div>
So the idea is when users passes a div with id="pgc-1" fire a function and so on for the rest of them.
Each of these divs has a li a item with the href attached, so I my function would look something like this
ga('send','event','scroll',city,$(this).text())
where this would be corresponding li a with the href
At the moments what I have is this.
A function to loop through div's and store their id's in array. And a build a li a menu.
var li="";
var linames = ["Intro","1925","1935","1945","1955","1965","1975","1985","1995","2005","Now"];
var i = 0;
function getSectionIDs()
{
$("div.panel-grid-cell").children().each(function() {
if(linames[i] !== undefined)
{
li += "<li><a href='#"+$(this).attr('id')+"'>"+linames[i]+"</a></li>";
}
i++;
});
$("ul.timeline-items").append(li);
}
Now I also have a function that checks how far did I scroll and change a class for each li item.
function onScroll(event){
var scrollPos = $(document).scrollTop();
$('ul.timeline-items li a').each(function () {
var currLink = $(this);
var refElement = $(currLink.attr("href"));
if (refElement.position().top -75 <= scrollPos && refElement.position().top+75 + refElement.height()-75 > scrollPos) {
$('ul.timeline-items li a').removeClass("active");
currLink.addClass("active");
}
else{
currLink.removeClass("active");
}
});
}
$(document).on("scroll", onScroll);
This Code does not what I want, because it constantly check If I have passed the div or not, but I need to fire my function only once.
Any help?
Found a solution myself the other day,
Inside a scrolling function just put a condition when $(document).scrollTop() equals to refElement.offset(), fire a function, and it works perfectly.
Meaning that check how far user has scrolled and if this value is equals to the offset of the div, fire a function.
I know this question have been asked a million times on this forum, but none of the articles helped me reach a solution.
I made a little piece of jquery code that highlights the hash-link when you scroll down to the section with the same id as in the hash-link.
$(window).scroll(function() {
var position = $(this).scrollTop();
$('.section').each(function() {
var target = $(this).offset().top;
var id = $(this).attr('id');
if (position >= target) {
$('#navigation > ul > li > a').attr('href', id).addClass('active');
}
});
});
The problem now is that it highlights all of the hash-links instead of just the one that the section has a relation to. Can anyone point out the mistake, or is it something that I forgot?
EDIT:
I have modified my answer to talk a little about performance and some particular cases.
If you are here just looking for code, there is a commented snippet at the bottom.
Original answer
Instead of adding the .active class to all the links, you should identify the one which attribute href is the same as the section's id.
Then you can add the .active class to that link and remove it from the rest.
if (position >= target) {
$('#navigation > ul > li > a').removeClass('active');
$('#navigation > ul > li > a[href=#' + id + ']').addClass('active');
}
With the above modification your code will correctly highlight the corresponding link. Hope it helps!
Improving performance
Even when this code will do its job, is far from being optimal. Anyway, remember:
We should forget about small efficiencies, say about 97% of the time:
premature optimization is the root of all evil. Yet we should not pass
up our opportunities in that critical 3%. (Donald Knuth)
So if, event testing in a slow device, you experience no performance issues, the best you can do is to stop reading and to think about the next amazing feature for your project!
There are, basically, three steps to improve the performance:
Make as much previous work as possible:
In order to avoid searching the DOM once and again (each time the event is triggered), you can cache your jQuery objects beforehand (e.g. on document.ready):
var $navigationLinks = $('#navigation > ul > li > a');
var $sections = $(".section");
Then, you can map each section to the corresponding navigation link:
var sectionIdTonavigationLink = {};
$sections.each( function(){
sectionIdTonavigationLink[ $(this).attr('id') ] = $('#navigation > ul > li > a[href=\\#' + $(this).attr('id') + ']');
});
Note the two backslashes in the anchor selector: the hash '#' has a special meaning in CSS so it must be escaped (thanks #Johnnie).
Also, you could cache the position of each section (Bootstrap's Scrollspy does it). But, if you do it, you need to remember to update them every time they change (the user resizes the window, new content is added via ajax, a subsection is expanded, etc).
Optimize the event handler:
Imagine that the user is scrolling inside one section: the active navigation link doesn't need to change. But if you look at the code above you will see that actually it changes several times. Before the correct link get highlighted, all the previous links will do it as well (because their corresponding sections also validate the condition position >= target).
One solution is to iterate the sections for the bottom to the top, the first one whose .offset().top is equal or smaller than $(window).scrollTop is the correct one. And yes, you can rely on jQuery returning the objects in the order of the DOM (since version 1.3.2). To iterate from bottom to top just select them in inverse order:
var $sections = $( $(".section").get().reverse() );
$sections.each( ... );
The double $() is necessary because get() returns DOM elements, not jQuery objects.
Once you have found the correct section, you should return false to exit the loop and avoid to check further sections.
Finally, you shouldn't do anything if the correct navigation link is already highlighted, so check it out:
if ( !$navigationLink.hasClass( 'active' ) ) {
$navigationLinks.removeClass('active');
$navigationLink.addClass('active');
}
Trigger the event as less as possible:
The most definitive way to prevent high-rated events (scroll, resize...) from making your site slow or unresponsive is to control how often the event handler is called: sure you don't need to check which link needs to be highlighted 100 times per second! If, besides the link highlighting, you add some fancy parallax effect you can ran fast intro troubles.
At this point, sure you want to read about throttle, debounce and requestAnimationFrame. This article is a nice lecture and give you a very good overview about three of them. For our case, throttling fits best our needs.
Basically, throttling enforces a minimum time interval between two function executions.
I have implemented a throttle function in the snippet. From there you can get more sophisticated, or even better, use a library like underscore.js or lodash (if you don't need the whole library you can always extract from there the throttle function).
Note: if you look around, you will find more simple throttle functions. Beware of them because they can miss the last event trigger (and that is the most important one!).
Particular cases:
I will not include these cases in the snippet, to not complicate it any further.
In the snippet below, the links will get highlighted when the section reaches the very top of the page. If you want them highlighted before, you can add a small offset in this way:
if (position + offset >= target) {
This is particullary useful when you have a top navigation bar.
And if your last section is too small to reach the top of the page, you can hightlight its corresponding link when the scrollbar is in its bottom-most position:
if ( $(window).scrollTop() >= $(document).height() - $(window).height() ) {
// highlight the last link
There are some browser support issues thought. You can read more about it here and here.
Snippet and test
Finally, here you have a commented snippet. Please note that I have changed the name of some variables to make them more descriptive.
// cache the navigation links
var $navigationLinks = $('#navigation > ul > li > a');
// cache (in reversed order) the sections
var $sections = $($(".section").get().reverse());
// map each section id to their corresponding navigation link
var sectionIdTonavigationLink = {};
$sections.each(function() {
var id = $(this).attr('id');
sectionIdTonavigationLink[id] = $('#navigation > ul > li > a[href=\\#' + id + ']');
});
// throttle function, enforces a minimum time interval
function throttle(fn, interval) {
var lastCall, timeoutId;
return function () {
var now = new Date().getTime();
if (lastCall && now < (lastCall + interval) ) {
// if we are inside the interval we wait
clearTimeout(timeoutId);
timeoutId = setTimeout(function () {
lastCall = now;
fn.call();
}, interval - (now - lastCall) );
} else {
// otherwise, we directly call the function
lastCall = now;
fn.call();
}
};
}
function highlightNavigation() {
// get the current vertical position of the scroll bar
var scrollPosition = $(window).scrollTop();
// iterate the sections
$sections.each(function() {
var currentSection = $(this);
// get the position of the section
var sectionTop = currentSection.offset().top;
// if the user has scrolled over the top of the section
if (scrollPosition >= sectionTop) {
// get the section id
var id = currentSection.attr('id');
// get the corresponding navigation link
var $navigationLink = sectionIdTonavigationLink[id];
// if the link is not active
if (!$navigationLink.hasClass('active')) {
// remove .active class from all the links
$navigationLinks.removeClass('active');
// add .active class to the current link
$navigationLink.addClass('active');
}
// we have found our section, so we return false to exit the each loop
return false;
}
});
}
$(window).scroll( throttle(highlightNavigation,100) );
// if you don't want to throttle the function use this instead:
// $(window).scroll( highlightNavigation );
#navigation {
position: fixed;
}
#sections {
position: absolute;
left: 150px;
}
.section {
height: 200px;
margin: 10px;
padding: 10px;
border: 1px dashed black;
}
#section5 {
height: 1000px;
}
.active {
background: red;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="navigation">
<ul>
<li>Section 1</li>
<li>Section 2</li>
<li>Section 3</li>
<li>Section 4</li>
<li>Section 5</li>
</ul>
</div>
<div id="sections">
<div id="section1" class="section">
I'm section 1
</div>
<div id="section2" class="section">
I'm section 2
</div>
<div id="section3" class="section">
I'm section 3
</div>
<div id="section4" class="section">
I'm section 4
</div>
<div id="section5" class="section">
I'm section 5
</div>
</div>
And in case you are interested, this fiddle tests the different improvements we have talked about.
Happy coding!
I've taken David's excellent code and removed all jQuery dependencies from it, in case anyone's interested:
// cache the navigation links
var $navigationLinks = document.querySelectorAll('nav > ul > li > a');
// cache (in reversed order) the sections
var $sections = document.getElementsByTagName('section');
// map each section id to their corresponding navigation link
var sectionIdTonavigationLink = {};
for (var i = $sections.length-1; i >= 0; i--) {
var id = $sections[i].id;
sectionIdTonavigationLink[id] = document.querySelectorAll('nav > ul > li > a[href=\\#' + id + ']') || null;
}
// throttle function, enforces a minimum time interval
function throttle(fn, interval) {
var lastCall, timeoutId;
return function () {
var now = new Date().getTime();
if (lastCall && now < (lastCall + interval) ) {
// if we are inside the interval we wait
clearTimeout(timeoutId);
timeoutId = setTimeout(function () {
lastCall = now;
fn.call();
}, interval - (now - lastCall) );
} else {
// otherwise, we directly call the function
lastCall = now;
fn.call();
}
};
}
function getOffset( el ) {
var _x = 0;
var _y = 0;
while( el && !isNaN( el.offsetLeft ) && !isNaN( el.offsetTop ) ) {
_x += el.offsetLeft - el.scrollLeft;
_y += el.offsetTop - el.scrollTop;
el = el.offsetParent;
}
return { top: _y, left: _x };
}
function highlightNavigation() {
// get the current vertical position of the scroll bar
var scrollPosition = window.pageYOffset || document.documentElement.scrollTop;
// iterate the sections
for (var i = $sections.length-1; i >= 0; i--) {
var currentSection = $sections[i];
// get the position of the section
var sectionTop = getOffset(currentSection).top;
// if the user has scrolled over the top of the section
if (scrollPosition >= sectionTop - 250) {
// get the section id
var id = currentSection.id;
// get the corresponding navigation link
var $navigationLink = sectionIdTonavigationLink[id];
// if the link is not active
if (typeof $navigationLink[0] !== 'undefined') {
if (!$navigationLink[0].classList.contains('active')) {
// remove .active class from all the links
for (i = 0; i < $navigationLinks.length; i++) {
$navigationLinks[i].className = $navigationLinks[i].className.replace(/ active/, '');
}
// add .active class to the current link
$navigationLink[0].className += (' active');
}
} else {
// remove .active class from all the links
for (i = 0; i < $navigationLinks.length; i++) {
$navigationLinks[i].className = $navigationLinks[i].className.replace(/ active/, '');
}
}
// we have found our section, so we return false to exit the each loop
return false;
}
}
}
window.addEventListener('scroll',throttle(highlightNavigation,150));
For anyone trying to use this solution more recently, I hit a snag trying to get it to work. You may need to escape the href like so:
$('#navigation > ul > li > a[href=\\#' + id + ']');
And now my browser doesn't throw an error on that piece.
function navHighlight() {
var scrollTop = $(document).scrollTop();
$("section").each(function () {
var xPos = $(this).position();
var sectionPos = xPos.top;
var sectionHeight = $(this).height();
var overall = scrollTop + sectionHeight;
if ((scrollTop + 20) >= sectionPos && scrollTop < overall) {
$(this).addClass("SectionActive");
$(this).prevAll().removeClass("SectionActive");
}
else if (scrollTop <= overall) {
$(this).removeClass("SectionActive");
}
var xIndex = $(".SectionActive").index();
var accIndex = xIndex + 1;
$("nav li:nth-child(" + accIndex + ")").addClass("navActivePage").siblings().removeClass("navActivePage");
});
}
.navActivePage {
color: #fdc166;
}
$(document).scroll(function () {
navHighlight();
});
In this line:
$('#navigation > ul > li > a').attr('href', id).addClass('active');
You are actually setting the href attribute of every $('#navigation > ul > li > a') element, and then adding the active class also to all of them. May be what you need to do is something like:
$('#navigation > ul > li > a[href=#' + id + ']')
And select only the a which href match the id. Make sense?
HTML:
<li class="home"><img alt="home" src="img/gohome.png"/></li>
<li class="portfolio closed" ><span>portfolio</span></li>
<li class="articles opened" style="margin-right: 849px;"><span>articles</span></li>
<li class="contact"><span>contact</span></li>
JS:
$('nav li').each(function(index) { //Navigation total width
navWidth += $(this).width();
});
I have script like that which works, but I also have to count width of Li elements till some specific element basing on class for ex. portfolio. And i don't have idea how to do it.
Another option with nextUntil():
$("nav li:first").nextUntil(".portfolio").andSelf().each(function(index) {
navWidth += $(this).width();
});
One way could be to exit the loop when you encounter an element with that class:
$('nav li').each(function() {
if ($(this).hasClass('portfolio')) {
return false;
}
navWidth += $(this).width();
});
Another way is to just select all the elements until the element with class portfolio. This can be done by getting the index of said element and select all elements up to that index:
var $lis = $('nav li');
$lis.slice(0, $lis.filter('.portfolio').index()).each(function() {
// ...
});
This is under the assumption that all those li elements are siblings of each other.
Reference: .each, .filter, .slice