Скачать или смотреть Resolving Issues with addEventListener and removeEventListener in JavaScript

Discover how to effectively manage `addEventListener` and `removeEventListener` in JavaScript, ensuring your event listeners work correctly without needing a page reload.
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This video is based on the question https://stackoverflow.com/q/63964040/ asked by the user 'Prestosaurus' ( https://stackoverflow.com/u/9302793/ ) and on the answer https://stackoverflow.com/a/63964186/ provided by the user 'Jason' ( https://stackoverflow.com/u/14268269/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving Issues with addEventListener and removeEventListener in JavaScript

When working with JavaScript, particularly with event listeners, developers often encounter a common problem: once an event listener is removed using removeEventListener, it does not respond again unless the page is reloaded. This issue can be frustrating for newcomers, especially if you're not entirely clear on the underlying mechanics of how these event listeners interact with each other. Let's dive into this problem and explore an effective solution.

Understanding the Problem

Many developers, especially those new to JavaScript, may find themselves removing event listeners but not realizing the implications of that action. When you use removeEventListener, the specific function that was originally passed to addEventListener is removed. Here’s a brief rundown of the terms involved:

addEventListener: This method is used to attach an event handler to a specified element.

removeEventListener: This method is used to detach an event handler from an element.

The Core Issue

In your initial code snippet, the mousedown event listener is removed after it has triggered. Once it's removed, it never gets added again, causing any subsequent mousedown events to go unrecognized. This leads to a frustrating experience where the dragging functionality ceases without a full page reload.

Solution Breakdown

To resolve this issue, you should ensure that the event listener intended to handle the mousedown event remains attached without being removed. Below is a reformulated approach to the problem using clear, organized functions, which improves readability and maintainability.

Revised Code Example

Here’s the updated version of your code that fixes the issue:

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

Key Changes Explained

Function Isolation: The core functions are separated into individual named functions (icHandleDrag, icResizeResize, and icStopDragging). This allows their references to persist and be reused without issues of being lost or removed.

Preserving mousedown Listener: The mousedown listener is maintained and never removed, which ensures the dragging functionality can be initiated multiple times without reloading.

Removing Only Necessary Listeners: The mousemove and mouseup listeners are removed when no longer needed, thus keeping the memory usage optimal and avoiding memory leaks.

Conclusion

By restructuring your event listener approach, you can overcome the challenges posed by removeEventListener and ensure your JavaScript event handling remains robust and responsive. This adjustment allows for seamless user interaction without requiring a page reload. Understanding how to effectively manage your event listeners is key to writing efficient JavaScript.

Remember, practice makes perfect, so keep experimenting with different event handling techniques!