How to Fix the addEventListener is Not a Function Error in JavaScript

Discover effective solutions to resolve the `addEventListener is not a function` error in your JavaScript code and improve your DOM event handling skills. --- This video is based on the question https://stackoverflow.com/q/69403014/ asked by the user 'Noob' ( https://stackoverflow.com/u/16816224/ ) and on the answer https://stackoverflow.com/a/69403313/ provided by the user 'Professor Abronsius' ( https://stackoverflow.com/u/3603681/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to fix .addEventListener is not a function Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- Troubleshooting the addEventListener is Not a Function Error in JavaScript As developers, we sometimes encounter frustrating errors that disrupt our workflow. One such problem is the infamous addEventListener is not a function error. This issue typically arises when working with JavaScript and handling DOM events, leaving many confused about how to resolve it. In this guide, we’ll dive into why this error occurs and how to fix it effectively. Understanding the Error The Uncaught TypeError: Cannot set property 'onclick' or addEventListener is not a function error can occur for several reasons. Most often, it arises when attempting to invoke a method on an object that is either undefined or not of the expected type. For example: [[See Video to Reveal this Text or Code Snippet]] In this instance, if btn is not a single DOM element (but rather a NodeList from querySelectorAll), you'll face this error. Why querySelectorAll Causes Issues The querySelectorAll method returns a NodeList containing all elements that match the specified selectors. Since NodeLists don't have addEventListener methods attached to them directly, trying to use this method results in the error we see. Here’s a visual breakdown: document.querySelectorAll(): Returns a collection of nodes (NodeList). document.querySelector(): Returns a single node or null. When selecting multiple elements with querySelectorAll, it is essential to iterate through each item to attach event listeners correctly. Solution: Iterating through NodeList To successfully bind an event to each button, you need to adjust your code to loop through the NodeList. Below is an improved version of the original code that handles events correctly. Revised Code Example [[See Video to Reveal this Text or Code Snippet]] [[See Video to Reveal this Text or Code Snippet]] Key Changes Made Introduced an iterable loop to go through each button element (btns.forEach). Simplified the query selector logic into concise functions for better readability. Added clear handling of different operations based on the button pressed using data-combine attributes. Conclusion Tackling errors in JavaScript can be daunting, but understanding the underlying causes and iterating through NodeLists can greatly enhance your ability to handle events effectively. By following the provided solution, you should now be able to eliminate the addEventListener is not a function error and create smooth, responsive user interactions. Remember, debugging is an essential part of coding, so continue experimenting and learning to strengthen your programming skills!