Javascript – Swap classes of an HTML element

Recently I came across the problem, that I had to programmatically change a div’s color from red to green. Sounds simple and it’s actually quite simple if you know your JavaScript.

jQuery contains a function called “toggleClass()” that swaps class attributes in and out of an element. I looked for a similar function in ES6 but couldn’t find one. Florian Brinkmann (@FloBrinkmann) pointed me to “classList.toggle()” which does exactly the thing I’m looking for (it’s hidden in the “Examples” passage).

Here’s the naive solution to my problem:

function toggleClass(element, className1, className2) {
  element
    .classList
    .toggle(className1);
  element
     .classList
     .toggle(className2);
 }

const myDiv = document.getElementById('myDiv'); 
toggleClass(myDiv, 'red', 'green');

The jQuery implementation contains the ability to define more than two classes to add or remove from the element. Using a new ES6 element (the spread operator) this can be implemented like this:

function toggleClass(element, ...classNames) {
{classNames.forEach((className) => {
  element
    .classList
    .toggle(className);
  })
}
toggleClass(myDiv, 'red', green', 'yellow');

jQuery's "toggleClass()" has some more functionality available but currently I don't have any need for it. For a start this is enough.