Скачать или смотреть Fixing the Uncaught TypeError: Cannot read property 'addEventListener' of null Error in JavaScript

Learn how to resolve the common error `Uncaught TypeError: Cannot read property 'addEventListener' of null` in your JavaScript code, ensuring that your interactive elements work smoothly.
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This video is based on the question https://stackoverflow.com/q/64623623/ asked by the user 'Pēteris No Jamaikas' ( https://stackoverflow.com/u/14554124/ ) and on the answer https://stackoverflow.com/a/64623683/ provided by the user 'سعيد' ( https://stackoverflow.com/u/13999386/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Uncaught TypeError in JavaScript

Are you developing a webpage and suddenly encounter the error Uncaught TypeError: Cannot read property 'addEventListener' of null? This frustration is common among developers, especially when they expect their interactive elements (like buttons or divs) to work seamlessly and nothing happens. If you’re trying to implement a sliding feature on a div and run into this problem, don’t worry! Here’s a straightforward explanation of the issue and how to resolve it.

The Problem Explained

The error you’re facing typically occurs because JavaScript is unable to find the specified element in the DOM (Document Object Model). In your case, the script attempts to add an event listener to the element with the class .arrow-div, but it fails because:

The selector you used doesn’t match any existing element.

The script runs before the HTML elements are fully loaded in the browser.

Here’s a snippet of your JavaScript code triggering the error:

[[See Video to Reveal this Text or Code Snippet]]

Now, let’s break down the solution step by step to eliminate this error.

Steps to Fix the Error

1. Use Correct Class Selectors

When using JavaScript's querySelector, it's mandatory to prepend a dot (.) for class selectors. Your original selectors were missing this dot.

Change the querySelector calls to the following:

[[See Video to Reveal this Text or Code Snippet]]

2. Ensure HTML Elements Are Loaded

Another common issue is that the script runs before the DOM is fully loaded. To ensure the DOM is ready, you can wrap your JavaScript code in an event listener for DOMContentLoaded:

[[See Video to Reveal this Text or Code Snippet]]

3. Final Code Adjustment

Here’s what the complete and corrected JavaScript will look like after implementing the changes:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By making these simple changes to your JavaScript code, you can fix the Uncaught TypeError error and make your interactive elements function correctly. Always remember to check that class selectors are accurately specified and that your scripts run after the DOM is fully loaded. Happy coding, and may your webpage's interactivity thrive!