TypeScript: Adding Multiple Classes to An Element

Updated: February 14, 2024 By: Guest Contributor Post a comment


TypeScript, a superset of JavaScript, offers not only strict typing but also enhanced syntax for manipulating the Document Object Model (DOM). A common task such as adding multiple classes to an HTML element can be approached in various ways with TypeScript, offering scalability and maintainability in web development projects.

Understanding DOM Manipulation in TypeScript

Before diving into the specifics of adding multiple classes, it’s essential to understand how TypeScript interacts with the DOM. Since TypeScript compiles down to JavaScript, all DOM manipulation in TypeScript is eventually executed as JavaScript. This means that any method available for DOM manipulation in JavaScript is also available in TypeScript, albeit with the added advantage of type checking and intellisense provided by TypeScript.

Example 1: Basic Class Addition

Let’s begin with the most straightforward example – adding a single class to an element. This establishes a foundation for understanding how to add multiple classes.

const element: HTMLElement | null = document.getElementById('myElement');
if (element) {

In the above example, we’ve safely accessed an HTML element by its ID and added a single class using the classList.add method. This method is safe and efficient but can be extended to add multiple classes.

Advanced Examples

As we progress, let’s explore more complex scenarios involving multiple classes.

Example 2: Adding Multiple Classes

if (element) {
  element.classList.add('class1', 'class2', 'class3');

This code snippet showcases the ability of the classList.add method to accept multiple arguments, each representing a class name to be added to the element. This is a clean and readable way to add several classes simultaneously.

Example 3: Conditional Class Addition

Sometimes, you might need to add classes based on certain conditions. TypeScript’s type checking can be especially helpful in these scenarios.

const isActive: boolean = true;
const isError: boolean = false;

if (element) {
  element.classList.add(...(isActive ? ['active'] : []), ...(isError ? ['error'] : []));

This technique uses the spread operator to conditionally add classes based on the boolean values of isActive and isError. It demonstrates TypeScript’s capability to integrate JavaScript features like the spread operator for more dynamic and conditional class manipulation.

Example 4: Employing TypeScript Interfaces for Dynamic Class Addition

For a more scalable and maintainable approach, especially in larger applications, leveraging TypeScript interfaces can be incredibly effective.

interface ClassOptions {
  active: boolean;
  error: boolean;
  highlight: boolean;

function updateElementClasses(element: HTMLElement, options: ClassOptions) {
  const { active, error, highlight } = options;
  element.classList.toggle('active', active);
  element.classList.toggle('error', error);
  element.classList.toggle('highlight', highlight);

if (element) {
  updateElementClasses(element, {
    active: true,
    error: false,
    highlight: true

This method introduces a reusable function updateElementClasses that accepts an element and an options object to dynamically add or remove classes. The classList.toggle method is utilized here, which adds the class if the second argument is true and removes it otherwise. This pattern is particularly useful in reactive interfaces or when the class state needs to be updated frequently based on user interaction or data changes.


Manipulating HTML elements’ classes through TypeScript provides robust, readable, and maintainable code solutions. The gradual increase in complexity from the basic adding of a single class to dynamically managing multiple classes based on conditions and interfaces reveals TypeScript’s power and flexibility in front-end development. Understanding these techniques can significantly enhance the quality of your projects, making your code more efficient and adaptable in the face of evolving web development practices.