Скачать или смотреть How to Fix a TypeError: Cannot read property 'value' of null in JavaScript

Discover how to resolve the frustrating TypeError in JavaScript that indicates a property is being accessed on a null value. Learn about common issues and their solutions.
---
This video is based on the question https://stackoverflow.com/q/68490872/ asked by the user 'Pablo Loes' ( https://stackoverflow.com/u/16401747/ ) and on the answer https://stackoverflow.com/a/68491069/ provided by the user 'John Adeniran' ( https://stackoverflow.com/u/6594090/ ) 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: Cannot read property 'value' of null function problem

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.
---
Understanding the TypeError: Cannot read property 'value' of null

When working with JavaScript, encountering errors can be frustrating—especially when you’re making progress on your project. One common issue developers face is the TypeError: Cannot read property 'value' of null. This error usually signifies that you are trying to access a property of an element that currently does not exist or is not accessible in the DOM (Document Object Model). In this post, we will break down the problem and explain how to effectively resolve it, allowing you to continue coding without unnecessary roadblocks.

The Problem

You might have come across this error when running a script that interacts with HTML elements. In the context provided, the error message was triggered on the addNumber function call, which suggests an issue with how JavaScript attempts to retrieve the value from an input element with the ID num. Here are some potential reasons for facing this issue:

The element with the ID num doesn’t exist in the HTML.

The JavaScript code runs before the DOM is fully loaded, making the element unavailable.

There might be typos or errors in your event listener setup.

Analyzing the Provided Code

Let’s dissect the provided snippet to identify where the issue might stem from:

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

Key Issues to Fix

Event Listener Typo:

The function addEventListenr is misspelled. Correct it to addEventListener to ensure the function works properly.

Element Retrieval:

Ensure that your HTML includes inputs with IDs addBtn, analyzeBtn, list, and num. If the element with ID num is not in your HTML, then this is why you're seeing the error—it would return null.

Function Parameter Count:

The isNumber function is expected to have two parameters but is defined to take one. The same applies to the inList function.

Solution Implementation

To fix the issues in the original code, consider the following corrected implementation:

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

Conclusion

By following the corrections outlined above, you can eliminate the pesky TypeError and ensure your JavaScript program runs smoothly. Always verify that the elements you are trying to manipulate exist in the DOM before executing code that depends on them. This practice, combined with proper debugging, will enhance your coding experience and produce better results!

If you continue to encounter issues or have any questions about JavaScript events, feel free to ask! Happy coding!