How to Make Your transitionend Event Work in JavaScript with Progress Elements

Discover how to properly implement CSS transitions for the ` progress ` element in JavaScript while ensuring your `transitionend` event fires correctly.
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Understanding the transitionend Event with Progress Elements

If you're diving into CSS transitions, you might encounter challenges when trying to trigger events after a transition ends, especially with HTML elements like <progress>. For instance, you might have encountered a scenario where your transitionend event does not fire even though you've set up transitions on your progress bar. In this guide, we'll explore why that happens and how you can fix it.

The Problem

While working on a user interface, you might want your progress element to visually convey the loading process. Ideally, you want to execute JavaScript functionality after the transition completes. However, many developers struggle with the transitionend event not firing on the <progress> element correctly when the value changes.

Common Mistake

When you set the value of the <progress> element using jQuery or JavaScript, like this:

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

The value updates instantly, and the transition may not be seen in the way you intend.

Why Doesn’t the transitionend Event Fire?

The core issue lies in understanding how the <progress> element and its CSS transitions work. The transition is applied to a pseudo-element, ::-webkit-progress-value, which is not directly accessible in the DOM. Therefore, manipulating the value of the progress bar doesn't create a clear transition effect that JavaScript can detect with the transitionend event.

Key Insight

When you change the value with .val(x), it doesn't trigger the transition, because the value change is instant. Thus, the transitionend event doesn't fire.

How to Fix It?

1. Remove the Transitions from Pseudo-elements

One immediate workaround is to eliminate transitions from the CSS rule applied to the pseudo-element. This ensures that value changes occur without attempting to animate, and therefore will not rely on the transitionend event to trigger actions.

Here's a minimal code sample demonstrating this approach:

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

Without transitions, the progress bar updates instantly, making any operations in your JavaScript fire immediately upon setting the value.

2. Use jQuery’s animate Method

A more refined approach would be to utilize the jQuery animate method instead. This approach can help create a smooth transition effect while providing proper callbacks.

Here’s how you can structure your code using animate:

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

This method allows you to create dynamic animations, handle completion callbacks, and provide feedback to the user without relying on the transitionend event.

CSS Example

Ensure your CSS remains functional and correctly styled for the transitions:

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

Conclusion

By recognizing the limitations of the <progress> element and employing jQuery's animate function, you can effectively manage transitions and make your JavaScript execute tasks at the right moments. Remember that understanding how each element responds to value changes and transitions is key to creating smooth user experiences.

Implement these strategies, and you'll find it much easier to handle transitions in your web projects!