Develop Reference

Function to check if element has any of these classes with native JS

<div id="test" class="a1 a2 a5"></div>
var element = document.getElementById("test")
if (hasAnyOfTheseClasses(element, ["a1", "a6"])) {
//...
}
Looking for a simple, lightweight function to check if a function has any of the listed classes without jQuery or another library.
Such function would be easy to implement, but there should be a canonical, fastest and simplest answer people can just copy-paste.
This seems vampire-ish, but I'm asking this so googlers won't have to write it themselves.
Not a duplicate - the linked question checks for one class, this question asks for checking any of the classes.
A jQuery version exists here.

Here's a functional implementation using Array.some and Element.classList.contains.
function hasAnyClass(element, classes) {
return classes.some(function(c) {
return element.classList.contains(c);
});
}
var div = document.getElementById("test");
console.log(hasAnyClass(div, ["hi", "xyz"]));
console.log(hasAnyClass(div, ["xyz", "there"]));
console.log(hasAnyClass(div, ["xyz", "xyz"]));
<div id="test" class="hi there"></div>
Note that these functions are not supported on older versions of IE, and will require a shim/polyfill.

You could use a regex, not sure that it's purely better but at least more flexible since your current test relies too much on spaces being entered correctly.
function hasAnyOfTheseClasses(element, classes) {
var className = element.className;
for (var i = 0; i < classes.length; i++) {
var exp = new RegExp('\b'+classes[i] + '\b');
if(exp.test(className)) return true;
}
return false;
}

just create a loop that check if each value in your array is a class in your passed element
function hasAnyOfTheseClasses(elem, tofind) {
classes = elem.className.split(' ');
for(var x in tofind) {
var className = tofind[x];
if (classes.indexOf(className) == -1){
return false;
}
}
return true;
}

Here's my implementation:
function hasAnyOfTheseClasses(element, classes) {
for (var i = 0; i < classes.length; i++) {
if ((' ' + element.className + ' ').indexOf(' ' + classes[i] + ' ') > -1) {
return true;
}
}
return false;
}
It's not elegant or fast. Works though. Feel free to edit to improve.

Use the .classList property to get the list of classes of an element. Then you can use the .contains() method to test each of the classes.
function hasAnyOfTheseClass(element, classes) {
var classList = element.classList;
return classes.some(function(class) {
return classList.contains(class);
});
}

How about using Array.prototype.some() and Array.prototype.indexOf():
function hasAnyClass(el, classes) {
var elClasses = el.className.split(' ');
return classes.some(c => elClasses.indexOf(c) >= 0)
}

Avoid double getElementId's within else if

I have a long list of else if statements.
Each one does a document.getElementById to check for existence of some element.
In one of of the else if statements to the bottom i need to not only do getElementById but I need to check also if that element has a certain attribute. This made me do getElementById twice, which i was hoping to avoid.
This is my code:
if (doc.getElementById('blah')) {
} else if (doc.getElementById('blah2')) {
} else if (doc.getElementById('js_blob') && doc.getElementById('js_blob').hasAttribute('action')) {
//here
} else if (doc.getElementById('blah3')) {
} else if (doc.getElementById('blah4')) {
} else {
console.warn('none of them');
}
Notice the line: } else if (doc.getElementById('js_blob') && doc.getElementById('js_blob').hasAttribute('action')) {
I had tried something like this and it didnt work: } else if (var myBlobL = doc.getElementById('js_blob') && myBlobL.hasAttribute('action')) { this would give syntax error
anyway to avoid doing double getElementById in this else if statement?
Thanks

Use a temporary variable:
var tmp;
// ...
} else if ((tmp = doc.getElementById('js_blob')) && tmp.hasAttribute('action')) {

You can save the result in a variable, in this case you only once will call getElementById
var js_blob = doc.getElementById('js_blob')
if (js_blob && js_blob.hasAttribute('action')) {
}
I see that you have logic with many "else if", I think you can replace it on something like this
function fn() {
var ids = ['elem1', 'elem2', 'elem3'],
len = ids.length,
i, el;
for (i = 0; i < len; i++) {
el = document.getElementById(ids[i]);
if (el) {
break;
}
}
if (!el) {
return;
}
// work with el which has action
// or add logic for specific ID
if (el.hasAttribute('action')) {
el.innerHTML = 'action';
} else if (el.getAttribute('id') === 'elem2') {
el.innerHTML = 'ELEM2';
}
}
fn();
Need decrease count appeals to the DOM, in this case you just once will appeal to each element, and further will work only with copy.

How to add and remove classes in Javascript without jQuery

I'm looking for a fast and secure way to add and remove classes from an html element without jQuery.
It also should be working in early IE (IE8 and up).

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");
Note: but not supported in IE <= 9 or Safari <=5.0

The following 3 functions work in browsers which don't support classList:
function hasClass(el, className)
{
if (el.classList)
return el.classList.contains(className);
return !!el.className.match(new RegExp('(\\s|^)' + className + '(\\s|$)'));
}
function addClass(el, className)
{
if (el.classList)
el.classList.add(className)
else if (!hasClass(el, className))
el.className += " " + className;
}
function removeClass(el, className)
{
if (el.classList)
el.classList.remove(className)
else if (hasClass(el, className))
{
var reg = new RegExp('(\\s|^)' + className + '(\\s|$)');
el.className = el.className.replace(reg, ' ');
}
}
https://jaketrent.com/post/addremove-classes-raw-javascript/

For future friendliness, I second the recommendation for classList with polyfill/shim: https://developer.mozilla.org/en-US/docs/Web/API/Element/classList#wrapper
var elem = document.getElementById( 'some-id' );
elem.classList.add('some-class'); // Add class
elem.classList.remove('some-other-class'); // Remove class
elem.classList.toggle('some-other-class'); // Add or remove class
if ( elem.classList.contains('some-third-class') ) { // Check for class
console.log('yep!');
}

classList is available from IE10 onwards, use that if you can.
element.classList.add("something");
element.classList.remove("some-class");

I'm baffled none of the answers here prominently mentions the incredibly useful DOMTokenList.prototype.toggle method, which really simplifies alot of code.
E.g. you often see code that does this:
if (element.classList.contains(className) {
element.classList.remove(className)
} else {
element.classList.add(className)
}
This can be replaced with a simple call to
element.classList.toggle(className)
What is also very helpful in many situations, if you are adding or removing a class name based on a condition, you can pass that condition as a second argument. If that argument is truthy, toggle acts as add, if it's falsy, it acts as though you called remove.
element.classList.toggle(className, condition) // add if condition truthy, otherwise remove

To add class without JQuery just append yourClassName to your element className
document.documentElement.className += " yourClassName";
To remove class you can use replace() function
document.documentElement.className.replace(/(?:^|\s)yourClassName(?!\S)/,'');
Also as #DavidThomas mentioned you'd need to use the new RegExp() constructor if you want to pass class names dynamically to the replace function.

Add & Remove Classes (tested on IE8+)
Add trim() to IE (taken from: .trim() in JavaScript not working in IE)
if(typeof String.prototype.trim !== 'function') {
String.prototype.trim = function() {
return this.replace(/^\s+|\s+$/g, '');
}
}
Add and Remove Classes:
function addClass(element,className) {
var currentClassName = element.getAttribute("class");
if (typeof currentClassName!== "undefined" && currentClassName) {
element.setAttribute("class",currentClassName + " "+ className);
}
else {
element.setAttribute("class",className);
}
}
function removeClass(element,className) {
var currentClassName = element.getAttribute("class");
if (typeof currentClassName!== "undefined" && currentClassName) {
var class2RemoveIndex = currentClassName.indexOf(className);
if (class2RemoveIndex != -1) {
var class2Remove = currentClassName.substr(class2RemoveIndex, className.length);
var updatedClassName = currentClassName.replace(class2Remove,"").trim();
element.setAttribute("class",updatedClassName);
}
}
else {
element.removeAttribute("class");
}
}
Usage:
var targetElement = document.getElementById("myElement");
addClass(targetElement,"someClass");
removeClass(targetElement,"someClass");
A working JSFIDDLE:
http://jsfiddle.net/fixit/bac2vuzh/1/

Try this:
const element = document.querySelector('#elementId');
if (element.classList.contains("classToBeRemoved")) {
element.classList.remove("classToBeRemoved");
}

I'm using this simple code for this task:
CSS Code
.demo {
background: tomato;
color: white;
}
Javascript code
function myFunction() {
/* Assign element to x variable by id */
var x = document.getElementById('para);
if (x.hasAttribute('class') {
x.removeAttribute('class');
} else {
x.setAttribute('class', 'demo');
}
}

Updated JS Class Method
The add methods do not add duplicate classes and the remove method only removes class with exact string match.
const addClass = (selector, classList) => {
const element = document.querySelector(selector);
const classes = classList.split(' ')
classes.forEach((item, id) => {
element.classList.add(item)
})
}
const removeClass = (selector, classList) => {
const element = document.querySelector(selector);
const classes = classList.split(' ')
classes.forEach((item, id) => {
element.classList.remove(item)
})
}
addClass('button.submit', 'text-white color-blue') // add text-white and color-blue classes
removeClass('#home .paragraph', 'text-red bold') // removes text-red and bold classes

You can also do
elem.classList[test ? 'add' : 'remove']('class-to-add-or-remove');
Instead of
if (test) {
elem.classList.add('class-to-add-or-remove');
} else {
elem.classList.remove('class-to-add-or-remove');
}

When you remove RegExp from the equation you leave a less "friendly" code, but it still can be done with the (much) less elegant way of split().
function removeClass(classString, toRemove) {
classes = classString.split(' ');
var out = Array();
for (var i=0; i<classes.length; i++) {
if (classes[i].length == 0) // double spaces can create empty elements
continue;
if (classes[i] == toRemove) // don't include this one
continue;
out.push(classes[i])
}
return out.join(' ');
}
This method is a lot bigger than a simple replace() but at least it can be used on older browsers. And in case the browser doesn't even support the split() command it's relatively easy to add it using prototype.

Just in case someone needs to toggle class on click and remove on other elements in JS only. You can try to do following :
var accordionIcon = document.querySelectorAll('.accordion-toggle');
//add only on first element, that was required in my case
accordionIcon[0].classList.add('close');
for (i = 0; i < accordionIcon.length; i++) {
accordionIcon[i].addEventListener("click", function(event) {
for (i = 0; i < accordionIcon.length; i++) {
if(accordionIcon[i] !== event.target){
accordionIcon[i].classList.remove('close');
}
event.target.classList.toggle("close");
}
})
}

How to determine if I'm selecting multiple or a single element with document.querySelector

I'm writing a function $ (similar to one of jQuery's $), but with non-jQuery methods and helpers, with plain DOM properties.
I have stucked at determining if I'm selecting multiple elements by a given selector or just a single element.
So far I have wrote this and I would like to know if there's a possibility to write this with less code and maybe only using only-one of the methods from DOM: querySelector or querySelectorAll.
String.prototype.startsWith = function( offset ) {
var _offset = 1;
if( offset !== undefined ) {
_offset = offset;
}
return this.substr(0, _offset);
}
function $( selector ) {
if( selector.startsWith() == '#') {
return document.querySelector( selector );
} else {
return document.querySelectorAll( selector );
}
}
How can we reduce the code of this?

function (selector) {
return document[selector[0] === '#' ?
'querySelector' :
'querySelectorAll'](selector)
}
Or you can do this:
function (selector) {
var result = document.querySelectorAll(selector);
if(result.length === 1)
return result[0];
return result;
}
EDIT jquery selectors always return array like object despite of item count in it, so what you are trying to do is different from jQuery behaviour

How do I parse the results of a querySelectorAll selector engine & allow method chaining?

SIMPLIFIED EXAMPLE CODE:
var $ = function(selector, node) { // Selector engine
var selector = selector.trim(), node = node || document.body;
if (selector != null) {
return Array.prototype.slice.call(node.querySelectorAll(selector), 0); }
}
}
I want to use it like this...:
$("div").innerHTML='It works!';
...not like this...:
$("div")[0].innerHTML='It works only on the specified index!';
...or this:
for(i=0;i<$('div');i++) {
$("div")[i].innerHTML='It works great but it's ugly!';
}
This is as close as I got. I would like chaining to work and for it to be compatible with native methods:
if(!Array.prototype.innerHTML) {
Array.prototype.innerHTML = function(html) {
for (var i = 0; i < this.length; i++) {
this[i].innerHTML = html;
}
}
}
$("div").innerHTML('It works, but it ruins method chaining!');
I decided to build this engine to better learn JavaScript; It's working but I am hoping I can learn some more from the kind members of Stack Overflow. Any help would be much appreciated!

I want to use it like this...:
$("div").innerHTML='It works!';
...not like this...:
$("div")[0].innerHTML='It works only on the specified index!';
It sounds like you want to have assigning to innerHTML on your set of results assign to the innerHTML of all of the results.
To do that, you'll have to use a function, either directly or indirectly.
Directly:
var $ = function(selector, node) { // Selector engine
var selector = selector.trim(),
node = node || document.body,
rv;
if (selector != null) {
rv = Array.prototype.slice.call(node.querySelectorAll(selector), 0); }
rv.setInnerHTML = setInnerHTML;
}
return rv;
}
function setInnerHTML(html) {
var index;
for (index = 0; index < this.length; ++index) {
this[index].innerHTML = html;
}
}
// Usage
$("div").setInnerHTML("The new HTML");
There, we define a function, and we assign it to the array you're returning as a property. You can then call that function on the array. (You might want to use Object.defineProperty if it's available to set the setInnerHTML property, so you can make it non-enumerable.)
Indirectly (requires an ES5-enabled JavaScript engine):
var $ = function(selector, node) { // Selector engine
var selector = selector.trim(),
node = node || document.body,
rv;
if (selector != null) {
rv = Array.prototype.slice.call(node.querySelectorAll(selector), 0); }
Object.defineProperty(rv, "innerHTML", {
set: setInnerHTML
});
}
return rv;
}
function setInnerHTML(html) {
var index;
for (index = 0; index < this.length; ++index) {
this[index].innerHTML = html;
}
}
// Usage
$("div").innerHTML = "The new HTML";
There, we use Object.defineProperty to define a setter for the property.
In the comments below you say
I have a few prototypes that work when individually attached to the $ function. Example: $('div').makeClass('this'); They do not work when they are chained together. Example: $('div').makeClass('this').takeClass('that');
To make chaining work, you do return this; from each of the functions (so the end of makeClass would do return this;). That's because when you're chaining, such as obj.foo().bar(), you're calling bar on the return value of foo. So to make chaining work, you make sure foo returns this (the object on which foo was called).

This is what works; it's a slightly different syntax then I gave in my prior example, but the end result is the same. I had some great help from other Stack Exchange members, thanks again everyone.
var $ = function(selector, node) { // Selector engine
var selector = selector.trim(), node = node || document.body;
if (selector != null) {
return Array.prototype.slice.call(node.querySelectorAll(selector), 0); }
}
}
if(!Array.prototype.html) {
Array.prototype.html = function(html) {
for (var i = 0; i < this.length; i++) {
this[i].innerHTML = html;
}
return this; //<---- Silly me, my original code was missing this.
}
}
When I run it, everything (including chaining) works as desired:
$("div").html('hello world');
OUTPUT:
<div>hello world</div>
Cheers!