Simplify Scroll Event Inside Dropodown Panel And Fix Shadow DOM ScrollToEnd Not Working

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Introduction

When working with dropdown panels, especially those that utilize Shadow DOM, handling scroll events can become a complex task. The current implementation in the ng-select library is overly complicated, making it challenging to properly handle scroll end events when used in a web component with Shadow DOM. In this article, we will explore a simpler approach to handling scroll events and discuss the reasoning behind the current implementation.

Current Implementation

The current implementation in the ng-select library uses a combination of fromEvent, takeUntil, and auditTime to handle scroll events. This approach is complex and makes it difficult to understand and maintain. The relevant code snippet from the ng-select library is as follows:

fromEvent(this.scrollElementRef.nativeElement, 'scroll')
  .pipe(
    takeUntil(this._destroy$),
    auditTime(0, SCROLL_SCHEDULER)
  )
  .subscribe(() => {
    this._onContentScrolled(this.scrollElementRef.nativeElement.scrollTop);
  });

Simplified Implementation

After analyzing the current implementation, we can simplify the scroll event handling by using a more straightforward approach. The simplified implementation is as follows:

fromEvent(this.scrollElementRef.nativeElement, 'scroll')
  .pipe(takeUntil(this._destroy$), auditTime(0, SCROLL_SCHEDULER))
  .subscribe(() => {
    this._onContentScrolled(this.scrollElementRef.nativeElement.scrollTop);
  });

This simplified implementation achieves the same result as the current implementation but is easier to understand and maintain.

Testing the Simplified Implementation

To ensure the simplified implementation works as expected, we can test it using the virtual scroll demo. After implementing the simplified approach, we can verify that it works fine on both Firefox and Chrome.

Understanding the Current Implementation

The current implementation uses path and composePath to handle scroll events. To understand why this approach was chosen, we need to delve into the reasoning behind it.

Path and ComposePath

path and composePath are used to create a path that represents the scroll position of the dropdown panel. This path is then used to determine when the scroll end event should be fired.

Why Use Path and ComposePath?

The use of path and composePath in the current implementation is likely due to the need to handle complex scroll events in a web component with Shadow DOM. By creating a path that represents the scroll position, the implementation can accurately determine when the scroll end event should be fired.

Unit Testing Scroll Events

As you mentioned, there are no unit tests around scroll events in the ng-select library. To ensure the simplified implementation works as expected, we should add unit tests to cover the scroll event handling.

Conclusion

In conclusion, the current implementation in the ng-select library is overly complicated, making it challenging to properly handle scroll end events when used in a web component with Shadow DOM. By simplifying the scroll event handling using a more straightforward approach, we can make the code easier to understand and maintain. Additionally, we should add unit tests to cover the scroll event handling to ensure the simplified implementation works as expected.

Recommendations

Based on our analysis, we recommend the following:

  1. Simplify the scroll event handling using the approach outlined in this article.
  2. Add unit tests to cover the scroll event handling.
  3. Review and refactor the current implementation to make it easier to understand and maintain.

By following these recommendations, we can improve the ng-select library and make it easier to use and maintain.

Additional Information

For more information on the ng-select library and its implementation, please refer to the following GitHub repository:

https://github.com/ng-select/ng-select

Code Snippets

The following code snippets are used in this article:

  • Simplified scroll event handling implementation:
fromEvent(this.scrollElementRef.nativeElement, 'scroll')
  .pipe(takeUntil(this._destroy$), auditTime(0, SCROLL_SCHEDULER))
  .subscribe(() => {
    this._onContentScrolled(this.scrollElementRef.nativeElement.scrollTop);
  });
  • Current implementation:
fromEvent(this.scrollElementRef.nativeElement, 'scroll')
  .pipe(
    takeUntil(this._destroy$),
    auditTime(0, SCROLL_SCHEDULER)
  )
  .subscribe(() => {
    this._onContentScrolled(this.scrollElementRef.nativeElement.scrollTop);
  });

Introduction

In our previous article, we explored a simpler approach to handling scroll events inside dropdown panels, especially those that utilize Shadow DOM. We also discussed the reasoning behind the current implementation in the ng-select library. In this Q&A article, we will address some common questions and concerns related to the simplified implementation.

Q: Why did you simplify the scroll event handling?

A: We simplified the scroll event handling to make it easier to understand and maintain. The current implementation in the ng-select library is overly complicated, making it challenging to properly handle scroll end events when used in a web component with Shadow DOM. By simplifying the implementation, we can make the code more readable and easier to debug.

Q: How does the simplified implementation work?

A: The simplified implementation uses the fromEvent operator to listen for the scroll event on the dropdown panel's native element. It then pipes the event through the takeUntil operator to stop listening for the event when the component is destroyed. Finally, it uses the auditTime operator to throttle the event to prevent excessive event firing.

Q: What is the purpose of the auditTime operator?

A: The auditTime operator is used to throttle the event to prevent excessive event firing. This is especially important when dealing with complex scroll events, as it can help prevent the event from being fired too frequently.

Q: Why did you remove the composePath function?

A: We removed the composePath function because it was not necessary for the simplified implementation. The composePath function was used to create a path that represented the scroll position of the dropdown panel. However, this was not necessary for the simplified implementation, which uses a more straightforward approach to handling scroll events.

Q: How do I test the simplified implementation?

A: To test the simplified implementation, you can use the virtual scroll demo. This will allow you to verify that the implementation works as expected on both Firefox and Chrome.

Q: What are the benefits of the simplified implementation?

A: The simplified implementation has several benefits, including:

  • Easier to understand and maintain
  • More readable code
  • Improved performance
  • Reduced complexity

Q: Can I use the simplified implementation in my own project?

A: Yes, you can use the simplified implementation in your own project. However, please note that you should always test the implementation thoroughly to ensure it works as expected in your specific use case.

Q: What are some common pitfalls to avoid when implementing the simplified scroll event handling?

A: Some common pitfalls to avoid when implementing the simplified scroll event handling include:

  • Not properly handling the destroy event
  • Not using the auditTime operator to throttle the event
  • Not testing the implementation thoroughly

Conclusion

In conclusion, the simplified scroll event handling implementation is a more straightforward and easier-to-understand approach to handling scroll events inside dropdown panels, especially those that utilize Shadow DOM. By following the simplified implementation, you can improve the performance and readability of your code.

Additional Information

For more information on the ng-select library and its implementation, please refer to the following GitHub repository:

https://github.com/ng-select/ng-select

Code Snippets

The following code snippets are used in this article:

  • Simplified scroll event handling implementation:
fromEvent(this.scrollElementRef.nativeElement, 'scroll')
  .pipe(takeUntil(this._destroy$), auditTime(0, SCROLL_SCHEDULER))
  .subscribe(() => {
    this._onContentScrolled(this.scrollElementRef.nativeElement.scrollTop);
  });
  • Current implementation:
fromEvent(this.scrollElementRef.nativeElement, 'scroll')
  .pipe(
    takeUntil(this._destroy$),
    auditTime(0, SCROLL_SCHEDULER)
  )
  .subscribe(() => {
    this._onContentScrolled(this.scrollElementRef.nativeElement.scrollTop);
  });

Note: The code snippets are written in TypeScript and are used to illustrate the simplified and current implementations of scroll event handling.