I have an element that already has a class:
<div class="someclass">
<img ... id="image1" name="image1" />
</div>
Now, I want to create a JavaScript function that will add a class to the div (not replace, but add).
How can I do that?
If you're only targeting modern browsers:
Use element.classList.add to add a class:
element.classList.add("my-class");
And element.classList.remove to remove a class:
element.classList.remove("my-class");
If you need to support Internet Explorer 9 or lower:
Add a space plus the name of your new class to the className property of the element. First, put an id on the element so you can easily get a reference.
<div id="div1" class="someclass">
<img ... id="image1" name="image1" />
</div>
Then
var d = document.getElementById("div1");
d.className += " otherclass";
Note the space before otherclass. It's important to include the space otherwise it compromises existing classes that come before it in the class list.
See also element.className on MDN.
The easiest way to do this without any framework is to use element.classList.add method.
var element = document.getElementById("div1");
element.classList.add("otherclass");
Edit:
And if you want to remove class from an element -
element.classList.remove("otherclass");
I prefer not having to add any empty space and duplicate entry handling myself (which is required when using the document.className approach). There are some browser limitations, but you can work around them using polyfills.
find your target element "d" however you wish and then:
d.className += ' additionalClass'; //note the space
you can wrap that in cleverer ways to check pre-existence, and check for space requirements etc..
Add Class
Cross Compatible
In the following example we add a classname to the <body> element. This is IE-8 compatible.
var a = document.body;
a.classList ? a.classList.add('classname') : a.className += ' classname';
This is shorthand for the following..
var a = document.body;
if (a.classList) {
a.classList.add('wait');
} else {
a.className += ' wait';
}
Performance
If your more concerned with performance over cross-compatibility you can shorten it to the following which is 4% faster.
var z = document.body;
document.body.classList.add('wait');
Convenience
Alternatively you could use jQuery but the resulting performance is significantly slower. 94% slower according to jsPerf
$('body').addClass('wait');
Removing the class
Performance
Using jQuery selectively is the best method for removing a class if your concerned with performance
var a = document.body, c = ' classname';
$(a).removeClass(c);
Without jQuery it's 32% slower
var a = document.body, c = ' classname';
a.className = a.className.replace( c, '' );
a.className = a.className + c;
References
jsPerf Test Case: Adding a Class
jsPerf Test Case: Removing a Class
Using Prototype
Element("document.body").ClassNames.add("classname")
Element("document.body").ClassNames.remove("classname")
Element("document.body").ClassNames.set("classname")
Using YUI
YAHOO.util.Dom.hasClass(document.body,"classname")
YAHOO.util.Dom.addClass(document.body,"classname")
YAHOO.util.Dom.removeClass(document.body,"classname")
Another approach to add the class to element using pure JavaScript
For adding class:
document.getElementById("div1").classList.add("classToBeAdded");
For removing class:
document.getElementById("div1").classList.remove("classToBeRemoved");
2 different ways to add class using JavaScript
JavaScript provides 2 different ways by which you can add classes to HTML elements:
Using element.classList.add() Method
Using className property
Using both methods you can add single or multiple classes at once.
1. Using element.classList.add() Method
var element = document.querySelector('.box');
// using add method
// adding single class
element.classList.add('color');
// adding multiple class
element.classList.add('border', 'shadow');
.box {
width: 200px;
height: 100px;
}
.color {
background: skyblue;
}
.border {
border: 2px solid black;
}
.shadow {
box-shadow: 5px 5px 5px gray;
}
<div class="box">My Box</div>
2. Using element.className Property
Note: Always use += operator and add a space before class name to add class with classList method.
var element = document.querySelector('.box');
// using className Property
// adding single class
element.className += ' color';
// adding multiple class
element.className += ' border shadow';
.box {
width: 200px;
height: 100px;
}
.color {
background: skyblue;
}
.border {
border: 2px solid black;
}
.shadow {
box-shadow: 5px 5px 5px gray;
}
<div class="box">My Box</div>
document.getElementById('some_id').className+=' someclassname'
OR:
document.getElementById('some_id').classList.add('someclassname')
First approach helped in adding the class when second approach didn't work.
Don't forget to keep a space in front of the ' someclassname' in the first approach.
For removal you can use:
document.getElementById('some_id').classList.remove('someclassname')
When the work I'm doing doesn't warrant using a library, I use these two functions:
function addClass( classname, element ) {
var cn = element.className;
//test for existance
if( cn.indexOf( classname ) != -1 ) {
return;
}
//add a space if the element already has class
if( cn != '' ) {
classname = ' '+classname;
}
element.className = cn+classname;
}
function removeClass( classname, element ) {
var cn = element.className;
var rxp = new RegExp( "\\s?\\b"+classname+"\\b", "g" );
cn = cn.replace( rxp, '' );
element.className = cn;
}
Assuming you're doing more than just adding this one class (eg, you've got asynchronous requests and so on going on as well), I'd recommend a library like Prototype or jQuery.
This will make just about everything you'll need to do (including this) very simple.
So let's say you've got jQuery on your page now, you could use code like this to add a class name to an element (on load, in this case):
$(document).ready( function() {
$('#div1').addClass( 'some_other_class' );
} );
Check out the jQuery API browser for other stuff.
You can use the classList.add OR classList.remove method to add/remove a class from a element.
var nameElem = document.getElementById("name")
nameElem.classList.add("anyclss")
The above code will add(and NOT replace) a class "anyclass" to nameElem.
Similarly you can use classList.remove() method to remove a class.
nameElem.classList.remove("anyclss")
To add an additional class to an element:
To add a class to an element, without removing/affecting existing values, append a space and the new classname, like so:
document.getElementById("MyElement").className += " MyClass";
To change all classes for an element:
To replace all existing classes with one or more new classes, set the className attribute:
document.getElementById("MyElement").className = "MyClass";
(You can use a space-delimited list to apply multiple classes.)
If you don't want to use jQuery and want to support older browsers:
function addClass(elem, clazz) {
if (!elemHasClass(elem, clazz)) {
elem.className += " " + clazz;
}
}
function elemHasClass(elem, clazz) {
return new RegExp("( |^)" + clazz + "( |$)").test(elem.className);
}
I too think that the fastest way is to use Element.prototype.classList as in es5: document.querySelector(".my.super-class").classList.add('new-class')
but in ie8 there is no such thing as Element.prototype.classList, anyway you can polyfill it with this snippet (fell free to edit and improve it):
if(Element.prototype.classList === void 0){
function DOMTokenList(classes, self){
typeof classes == "string" && (classes = classes.split(' '))
while(this.length){
Array.prototype.pop.apply(this);
}
Array.prototype.push.apply(this, classes);
this.__self__ = this.__self__ || self
}
DOMTokenList.prototype.item = function (index){
return this[index];
}
DOMTokenList.prototype.contains = function (myClass){
for(var i = this.length - 1; i >= 0 ; i--){
if(this[i] === myClass){
return true;
}
}
return false
}
DOMTokenList.prototype.add = function (newClass){
if(this.contains(newClass)){
return;
}
this.__self__.className += (this.__self__.className?" ":"")+newClass;
DOMTokenList.call(this, this.__self__.className)
}
DOMTokenList.prototype.remove = function (oldClass){
if(!this.contains(newClass)){
return;
}
this[this.indexOf(oldClass)] = undefined
this.__self__.className = this.join(' ').replace(/ +/, ' ')
DOMTokenList.call(this, this.__self__.className)
}
DOMTokenList.prototype.toggle = function (aClass){
this[this.contains(aClass)? 'remove' : 'add'](aClass)
return this.contains(aClass);
}
DOMTokenList.prototype.replace = function (oldClass, newClass){
this.contains(oldClass) && this.remove(oldClass) && this.add(newClass)
}
Object.defineProperty(Element.prototype, 'classList', {
get: function() {
return new DOMTokenList( this.className, this );
},
enumerable: false
})
}
To add, remove or check element classes in a simple way:
var uclass = {
exists: function(elem,className){var p = new RegExp('(^| )'+className+'( |$)');return (elem.className && elem.className.match(p));},
add: function(elem,className){if(uclass.exists(elem,className)){return true;}elem.className += ' '+className;},
remove: function(elem,className){var c = elem.className;var p = new RegExp('(^| )'+className+'( |$)');c = c.replace(p,' ').replace(/ /g,' ');elem.className = c;}
};
var elem = document.getElementById('someElem');
//Add a class, only if not exists yet.
uclass.add(elem,'someClass');
//Remove class
uclass.remove(elem,'someClass');
I know IE9 is shutdown officially and we can achieve it with element.classList as many told above but I just tried to learn how it works without classList with help of many answers above I could learn it.
Below code extends many answers above and improves them by avoiding adding duplicate classes.
function addClass(element,className){
var classArray = className.split(' ');
classArray.forEach(function (className) {
if(!hasClass(element,className)){
element.className += " "+className;
}
});
}
//this will add 5 only once
addClass(document.querySelector('#getbyid'),'3 4 5 5 5');
You can use modern approach similar to jQuery
If you need to change only one element, first one that JS will find in DOM, you can use this:
document.querySelector('.someclass').className += " red";
.red {
color: red;
}
<div class="someclass">
<p>This method will add class "red" only to first element in DOM</p>
</div>
<div class="someclass">
<p>lorem ipsum</p>
</div>
<div class="someclass">
<p>lorem ipsum</p>
</div>
<div class="someclass">
<p>lorem ipsum</p>
</div>
Keep in mind to leave one space before class name.
If you have multiple classes where you want to add new class, you can use it like this
document.querySelectorAll('.someclass').forEach(function(element) {
element.className += " red";
});
.red {
color: red;
}
<div class="someclass">
<p>This method will add class "red" to all elements in DOM that have "someclass" class.</p>
</div>
<div class="someclass">
<p>lorem ipsum</p>
</div>
<div class="someclass">
<p>lorem ipsum</p>
</div>
<div class="someclass">
<p>lorem ipsum</p>
</div>
This might be helpful for WordPress developers etc.
document.querySelector('[data-section="section-hb-button-1"] .ast-custom-button').classList.add('TryMyClass');
Just to elaborate on what others have said, multiple CSS classes are combined in a single string, delimited by spaces. Thus, if you wanted to hard-code it, it would simply look like this:
<div class="someClass otherClass yetAnotherClass">
<img ... id="image1" name="image1" />
</div>
From there you can easily derive the javascript necessary to add a new class... just append a space followed by the new class to the element's className property. Knowing this, you can also write a function to remove a class later should the need arise.
I think it's better to use pure JavaScript, which we can run on the DOM of the Browser.
Here is the functional way to use it. I have used ES6 but feel free to use ES5 and function expression or function definition, whichever suits your JavaScript StyleGuide.
'use strict'
const oldAdd = (element, className) => {
let classes = element.className.split(' ')
if (classes.indexOf(className) < 0) {
classes.push(className)
}
element.className = classes.join(' ')
}
const oldRemove = (element, className) => {
let classes = element.className.split(' ')
const idx = classes.indexOf(className)
if (idx > -1) {
classes.splice(idx, 1)
}
element.className = classes.join(' ')
}
const addClass = (element, className) => {
if (element.classList) {
element.classList.add(className)
} else {
oldAdd(element, className)
}
}
const removeClass = (element, className) => {
if (element.classList) {
element.classList.remove(className)
} else {
oldRemove(element, className)
}
}
Sample with pure JS. In first example we get our element's id and add e.g. 2 classes.
document.addEventListener('DOMContentLoaded', function() {
document.getElementsById('tabGroup').className = "anyClass1 anyClass2";
})
In second example we get element's class name and add 1 more.
document.addEventListener('DOMContentLoaded', function() {
document.getElementsByClassName('tabGroup')[0].className = "tabGroup ready";
})
For those using Lodash and wanting to update className string:
// get element reference
var elem = document.getElementById('myElement');
// add some classes. Eg. 'nav' and 'nav header'
elem.className = _.chain(elem.className).split(/[\s]+/).union(['nav','navHeader']).join(' ').value()
// remove the added classes
elem.className = _.chain(elem.className).split(/[\s]+/).difference(['nav','navHeader']).join(' ').value()
Shortest
image1.parentNode.className+=' box';
image1.parentNode.className+=' box';
.box { width: 100px; height:100px; background: red; }
<div class="someclass">
<img ... id="image1" name="image1" />
</div>
You can use the API querySelector to select your element and then create a function with the element and the new classname as parameters. Using classlist for modern browsers, else for IE8. Then you can call the function after an event.
//select the dom element
var addClassVar = document.querySelector('.someclass');
//define the addclass function
var addClass = function(el,className){
if (el.classList){
el.classList.add(className);
}
else {
el.className += ' ' + className;
}
};
//call the function
addClass(addClassVar, 'newClass');
In my case, I had more than one class called main-wrapper in the DOM, but I only wanted to affect the parent main-wrapper. Using :first Selector (https://api.jquery.com/first-selector/), I could select the first matched DOM element. This was the solution for me:
$(document).ready( function() {
$('.main-wrapper:first').addClass('homepage-redesign');
$('#deals-index > div:eq(0) > div:eq(1)').addClass('doubleheaderredesign');
} );
I also did the same thing for the second children of a specific div in my DOM as you can see in the code where I used $('#deals-index > div:eq(0) > div:eq(1)').addClass('doubleheaderredesign');.
NOTE: I used jQuery as you can see.
The majority of people use a .classList.add on a getElementById, but I i wanted to use it on a getElementByClassName. To do that, i was using a forEach like this :
document.getElementsByClassName("class-name").forEach(element => element.classList.add("new-class"));
But it didn't work because i discovered that getElementsByClassName returns a HTML collection and not an array. To handle that I converted it to an array with this code :
[...document.getElementsByClassName("class-name")].forEach(element => element.classList.add("new-class"));
first, give the div an id. Then, call function appendClass:
<script language="javascript">
function appendClass(elementId, classToAppend){
var oldClass = document.getElementById(elementId).getAttribute("class");
if (oldClass.indexOf(classToAdd) == -1)
{
document.getElementById(elementId).setAttribute("class", classToAppend);
}
}
</script>
This js code works for me
provides classname replacement
var DDCdiv = hEle.getElementBy.....
var cssCNs = DDCdiv.getAttribute('class');
var Ta = cssCNs.split(' '); //split into an array
for (var i=0; i< Ta.length;i++)
{
if (Ta[i] == 'visible'){
Ta[i] = 'hidden';
break;// quit for loop
}
else if (Ta[i] == 'hidden'){
Ta[i] = 'visible';
break;// quit for loop
}
}
DDCdiv.setAttribute('class',Ta.join(' ') ); // Join array with space and set class name
To add just use
var cssCNs = DDCdiv.getAttribute('class');
var Ta = cssCNs.split(' '); //split into an array
Ta.push('New class name');
// Ta.push('Another class name');//etc...
DDCdiv.setAttribute('class',Ta.join(' ') ); // Join array with space and set class name
To remove use
var cssCNs = DDCdiv.getAttribute('class');
var Ta = cssCNs.split(' '); //split into an array
for (var i=0; i< Ta.length;i++)
{
if (Ta[i] == 'visible'){
Ta.splice( i, 1 );
break;// quit for loop
}
}
DDCdiv.setAttribute('class',Ta.join(' ') ); // Join array with space and set class name
Hope this is helpful to sombody
In YUI, if you include yuidom, you can use
YAHOO.util.Dom.addClass('div1','className');
HTH
I have my code below:
<ul id="profileList" class="nav nav-list">
<li>修改个人签名档</li>
<li>修改个人居住地</li>
<li>修改个人学校专业</li>
</ul>
Also here's the JS code:
<script type="text/javascript">
$(document).ready(function() {
// store url for current page as global variable
current_page = document.location.href
// apply selected states depending on current page
if (current_page.index(/signature/)) {
$("ul#profileList li:eq(0)").addClass('active');
} else if (current_page.match(/location/)) {
$("ul#profileList li:eq(1)").addClass('active');
} else if (current_page.match(/education/)) {
$("ul#profileList li:eq(2)").addClass('active');
} else { // don't mark any nav links as selected
$("ul#profileList li").removeClass('active');
};
});
</script>
When I click the second and third li item, they work well. But when I click the first item,
the item is not becoming active. What's the wrong and why?
In
if (current_page.index(/signature/)) {
Change to
if (current_page.match(/signature/)) {
As far as I know, String.prototype.index doesn't exist. Perhaps you wanted to use the indexOf method.
if (current_page.indexOf('signature') !== -1) {}
Also, do not use the String.prototype.match function when you just want to know if there's a match or not, use the RegExp.prototype.test function.
if (/education/.test('education')) { /*matches*/ }
However in your case, you could use the match method and instead of discarding the match, use it at your advantage:
var sections = ['signature', 'location', 'education'],
match = document.location.href.match(new RegExp(sections.join('|'), 'i')),
selectorSuffix = match? ':eq(' + sections.indexOf(match[0].toLowerCase()) + ')' : '';
$('ul#profileList li' + selectorSuffix)[(match? 'add' : 'remove') + 'Class']('active');
I would like to prevent duplicate classnames on an element using JavaScript.
When I run the following code, I get the classname "Test 1" twice.
Here's my HTML:
<body>
<div id="foo">Hey</div>
</body>
and my Javascript:
function addClass(element, myClass) {
var add = element.className += ' ' + myClass;
}
addClass(foo,'Test1');
addClass(foo,'Test1');
addClass(foo, 'Test2');
I would like my result to be:
<div id="foo" class=" Test1 Test2">Hey</div>
and not
<div id="foo" class=" Test1 Test1 Test2">Hey</div>
Is there any way I can achieve this?
Use the string.contains() method when adding the class; try something like
function addClass(element, myClass) {
if(!element.className.contains(myClass))
element.className += ' ' + myClass;
}
EDIT
Use string.split(" ") to break the class names up (to avoid matching partial class names), then use indexOf to check to see if the class has been added already. Something like
function addClass(element, myClass) {
if(element.className.split(" ").indexOf(myClass)==-1)
element.className += ' ' + myClass;
}
jsFiddle here.
Use indexOf() to see if it already has that class. Note that the solution by itself would cause problems when having classes that contain part of another, so I've slightly changed it (New solution is a little ugly but meh)
function addClass(element, myClass) {
if((" " +element.className+ " ").indexOf(" "+myClass+" ") == -1)
element.className += ' ' + myClass;
}
I suppose if you are adding a class you want that class to have precedence- if it exists already but was superceded in the cascade by another class, move the old instance to the end of the class definitition-
function addCLass(who,cname){
var rx= RegExp('\\b'+cname+'\\b','g'),
C=who.className.replace(rx,'').split(/\s+/).push(cname);
who.className= C.join(' ');
}
I have some HTML elements which I want to validate whether they fit within their parent elements width. Basically, I dont want any of the child container elements to exceed the parent elements width. for example:
<div id="parent" style="width:100px;">
<div id="child" style="width:120px;"> //wrong
</div>
with a large html page and multiple developers working, if a new element is added which violates this rule, the page alignment collapse. is there an js where i can tell validate this child element, and run the page on DOM, to check if the element succeeds this test
You shouldn't use javascript for it. The best solution is a good CSS pattern for your project.
But yes, you can validade the objects.
Something like this:
function validateParent(element, prop, callback) {
var parentProp = element.parentElement.style[prop];
var childProp = element.style[prop];
if(parseFloat(childProp) > parseFloat(parentProp)) {
// do something here like execute the callback
if(typeof callback === 'function') {
callback.call(element, prop, parentProp);
}
}
}
Using example:
// make the children value equals the parent
validateParent(document.getElementById('foo'), 'width', function(prop, val) {
this.style[prop] = val;
});
// Dispatch an alert
validateParent(document.getElementById('foo'), 'width', function(prop, val) {
alert('The value from ' + this.id + ' is bigger then it parent, that is ' + val;
});