DOM - Class attribute

HTML - The class attribute manipulation in the DOM.

The DOM Web API has a special function to select on class: the getElementsByClassName() function

You can select the class with a selector

• With Native Javascript

// the first one
document.querySelector(".myclass");
// All
document.querySelectorAll(".myclass");

• With Jquery

$('.myclass')

How to select an element that contains two class values.

• The HTML with two paragraph, we want to select only the second one (ie the one with the values first and second)

<p class="first">Paragraph with one class value</p>
<p class="first second">The Paragraph with two class values should be in red</p>

• The javascript that select the element and add a red color style

let element = document.querySelector(".first.second");
element.style.setProperty('color', 'red');

• Output:

Jquery HasClass

• Native javascript

<div class="foo bar"></div>

element = document.querySelector(".bar");
console.log("Is the class foo present ? "+ element.classList.contains("foo"));

toggle (or toggling) means to:

• add a class if not present
• or delete it if present

The DOMTokenList/toggle:

element.classList.toggle("className")

// The same as
if (element.classList.contains("className")){
    element.classList.remove("className");
} else {
    element.classList.add("className");
}

A demo with Native Javascript

• A css with the toggle class that we are going to toggle.

.toggle {
  color:blue;
}

• A button that we will click to toggle its class

<button class="toggle" src="#">Toggled</button>

• The javascript:
  • select all button
  • add a event listener on click
  • that toggles the class

document.querySelectorAll("button").forEach(element => {
   element.addEventListener("click", function () {
        result = element.classList.toggle("toggle");
        if (result){
            element.innerText = "Toggled";
        } else {
            element.innerText = "UnToggled";
        }
   });
});

• Try it: click on the button.

• after selection of one element

document.getElementById(Id).classList.add('is-shown','is-blue')
document.querySelector('.js-nav').classList.add('is-shown')

• As class string

document.querySelector('.js-nav').classList.add('is-shown is-blue'.split(' '))

• to an html element target of an event

event.target.classList.add('is-selected')

With the addClass Jquery Method

• The CSS that will apply the color blueviolet to all element with a beauty-blue class

.beauty-blue { color: blueviolet; }

• the Javascript that adds the class beauty blue with the addClass Jquery Method

$( "p" ).addClass( "beauty-blue" )

• the HTML where the p element will get the class beauty-blue at runtime via javascript.

<p>The text should be blue violet because the class 'beauty-blue' was added at runtime</p>

• The result:

You can control it by looking the DOM element with the devtool.

Example: with chrome:

document.getElementById(Id).classList.remove('is-shown')

With the removeClass Jquery Method

• the Javascript that remove the class beauty blue with the removeClass Jquery Method

$( "p" ).removeClass( "beauty-blue" )

• the HTML where the p element will get the class beauty-blue at runtime via javascript.

<p class="beauty-blue">The text should be black because the class 'beauty-blue' was removed</p>

• A Css that will never be applied because the class will be remove by Javacript

.beauty-blue { color: blueviolet; }

• The result:

You can control it by looking the DOM element with the devtool.

Example: with chrome: