How to Select Elements with Multiple Classes – Master JavaScript for A/B Testing

Select Elements with Multiple Class:

This post is part of mastering JavaScript for A/B Testing. As a marketer involved in experimentation programs, having a good understanding of JavaScript can greatly enhance your ability to optimize and personalize user experiences. One fundamental skill is selecting HTML elements with multiple classes using JavaScript. In this blog post, we will walk you through the step-by-step process of selecting elements with multiple classes and explain why and how it’s done. So, let’s dive in!

Step 1: Understanding the Importance of Selecting Elements with Multiple Classes
When working on experiments, you often need to target specific elements on a webpage to apply changes or measure their performance. Elements with 0multiple classes offer a more granular way of selecting and manipulating these elements, allowing for precise targeting and styling.

Step 2: Identifying the Targeted Element
Before we can select an element with multiple classes, we need to identify it within the HTML structure. Inspect the webpage using your browser’s developer tools to find the element you want to select. Take note of its unique combination of classes.

Step 3: Using the Document Object Model (DOM)
The DOM is a programming interface that represents the structure of an HTML document. It allows JavaScript to interact with and manipulate the document’s elements. To select an element with multiple classes, we utilize the DOM’s querySelector method.

Step 4: Constructing the Selector
To select an element with multiple classes, we build a CSS selector using the desired classes. The CSS selector syntax combines class names with a dot (.), indicating that the element must have all specified classes to be selected.

Suppose we want to select an element with classes “experiment” and “cta-button”. We can construct the selector as follows:

const element = document.querySelector('.experiment.cta-button');

In the example above, we’ve used the dot (.) to concatenate the classes “experiment” and “cta-button”.

Step 5: Applying Actions to the Selected Element
Once we’ve successfully selected the element, we can apply various actions to it. For instance, we can modify its content, change its styling, attach event listeners, or track user interactions.

Let’s assume we want to change the background color of the selected element to red. We can do so by adding the following JavaScript code: = 'red';


Here’s an example scenario to illustrate selecting an element with multiple classes using JavaScript:

Let’s say you’re working on an experimentation program for an e-commerce website, and you want to highlight a specific button that encourages users to sign up for a newsletter. The button has two classes: “btn” and “newsletter-signup”.

  1. Identify the Targeted Element:
    Inspect the webpage using your browser’s developer tools and locate the HTML element representing the newsletter signup button. Note down the classes assigned to it: “btn” and “newsletter-signup”.
  2. Use the Document Object Model (DOM):
    To interact with the webpage’s elements, we’ll use JavaScript and the DOM. Start by including the JavaScript code in your webpage or experiment script.
  3. Construct the Selector:
    Construct a CSS selector using the desired classes, separated by a dot (.) to indicate that the element must have both classes to be selected. In this case, the selector would be “.btn.newsletter-signup”.
  4. Select and Modify the Element:
    To select the button element, use the querySelector method and assign it to a variable. Then, you can modify its properties, such as changing its background color.
// Select the element with classes "btn" and "newsletter-signup"
const buttonElement = document.querySelector('.btn.newsletter-signup');

// Apply changes to the selected element = 'red';

In the example above, we first select the element using the constructed selector “.btn.newsletter-signup”. Then, we assign it to the variable buttonElement. Finally, we modify the background color of the button to red by accessing the style property and setting the backgroundColor property.

By using JavaScript to select elements with multiple classes, you can easily target specific elements and apply changes or track their performance in your marketing experiments.


Selecting elements with multiple classes in JavaScript opens up a world of possibilities for marketers engaged in experimentation programs. By understanding the DOM and utilizing the querySelector method, you can confidently target and manipulate specific elements on a webpage. Remember to construct the selector with the desired classes and apply actions to the selected element using JavaScript. With these skills in your toolkit, you’ll be well-equipped to optimize and personalize user experiences through experimentation.

We hope this step-by-step guide has provided you with the knowledge and confidence to harness the power of JavaScript in your marketing experiments. Happy experimenting!

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