Скачать или смотреть Understanding the Vue Infinite Loop Bug: How to Fix Your Refresh Cycle

Discover the common pitfall of an infinite refresh loop in Vue.js and learn how to resolve it effortlessly with an easy-to-understand guide.
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This video is based on the question https://stackoverflow.com/q/76343209/ asked by the user 'Stephen Rich' ( https://stackoverflow.com/u/12121864/ ) and on the answer https://stackoverflow.com/a/76343502/ provided by the user 'Moritz Ringler' ( https://stackoverflow.com/u/4883195/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Vue Infinite Loop Bug: How to Fix Your Refresh Cycle

When working on Vue.js applications, developers can occasionally encounter a frustrating problem: an infinite refresh loop. This issue can manifest when you have a component setup that triggers continuous rendering updates, often leading to confusion and anxiety over whether it's a bug or misconfiguration.

In this guide, we’ll explore a specific scenario that leads to this infinite loop, breaking down the core problem and leading you step-by-step through the solution, so that you can confidently avoid this issue in the future.

The Problem: Infinite Refresh Loop

Consider the following situation: You have a parent component that passes an object through a prop to a child component. When you attempt to render a variable (like a counter) in your parent component, you notice that it leads to an endless loop of refreshes.

Example Components

Here’s a simplified version of what your code might look like:

App.vue:

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

HelloWorld.vue:

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

When you uncomment the line that displays the {{counter}} in App.vue, you trigger an infinite loop.

The Cause of the Infinite Loop

This issue arises from how the :scope prop is managed. Within HelloWorld, you're watching for changes to the scope prop and emitting a counter event whenever there’s an update. However, the key problem lies in this line in App.vue:

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

Why It Causes an Infinite Loop

New Object Creation: Each time the parent component is re-rendered, a new empty object {} is created and passed as a prop to HelloWorld.

Watcher Activation: Since the watcher on scope detects this change (as it sees a new object rather than the same reference), it triggers the handler.

Event Emission: The handler in HelloWorld invokes this.update(), which increments the counter and emits it back to the parent.

Parent Redraw: The parent component reacts to the emitted event, resulting in another re-render.

This cycle continues indefinitely, similar to what's caused by a while (true) loop—resulting not from a bug in Vue but from the use of unique, throw-away objects.

The Solution: Use a Static Object Reference

To eliminate the infinite loop, simply use a shared variable instead of a new object. Here’s how you can do it:

Define a Constant:
In your App.vue, create a constant object:

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

Modify the Prop Binding:
Pass the constant object to the child component:

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

By doing this, the reference for scope remains the same during re-renders, and the watcher doesn't trigger, thus breaking the infinite loop.

Conclusion

Encountering an infinite loop while working with Vue can be daunting, but understanding the mechanics behind how Vue's reactivity works is crucial. This issue isn’t a bug—it arises from how you're passing props and is solvable with a simple adjustment.

Next time you run into this issue, remember to check your prop references and aim for stable objects rather than newly created ones. Happy coding!