Solving Infinite Loops in Angular 6: A Guide to Async Function Calls

Find out how to avoid `infinite loops` when making API calls in Angular 6 templates. We'll break down the solutions and provide clear examples!
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Solving Infinite Loops in Angular 6: A Guide to Async Function Calls

When working with Angular, you may encounter a challenging issue: an infinite loop that arises from calling a function within your template. This problem typically occurs when you perform asynchronous operations, such as API calls, and try to display their results directly in the HTML. In this guide, we'll walk you through the root cause of this issue and provide practical solutions to avoid it.

Understanding the Problem

Imagine you're trying to display data fetched asynchronously in your Angular component. Here's an outline of what might go wrong:

You have an ngFor loop that iterates over a collection of data.

Within this loop, you call a function that makes an asynchronous API call and returns a promise or observable.

This results in the template continually re-evaluating the function, leading to an infinite loop.

Sample Code Structure

To illustrate, let's look at a simplified version of how this issue might arise in code:

sample.html

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

sample.component.ts

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

The makeApiCall(i) function is intended to fetch data from an API and return the response. However, as you may notice, it triggers an error: Cannot read property 'makeApiCall' of undefined.

Diagnosing the Cause of the Error

The error occurs because the this context inside the Promise is not bound to the Angular component but instead refers to the function itself. This is the heart of the issue, leading to the infinite call cycle as Angular continuously checks for changes.

Proposed Solution

Using Arrow Functions

To fix this issue, you can change the way you define your promise function. By using an arrow function, you can maintain the lexical scope of this, ensuring it refers to your Angular component rather than the promise itself.

Here's how to implement that:

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

Why This Works

Arrow Functions: When you use an arrow function, this retains the context of the enclosing scope, which is your Angular component class. This prevents the undefined error and avoids the infinite loop.

Change Detection Strategy: Using ChangeDetectionStrategy.OnPush can be very effective, as it tells Angular to check the component for changes only when its inputs change or you manually trigger change detection using cd.detectChanges().

Conclusion

Handling asynchronous function calls in Angular templates can lead to frustrating issues like infinite loops, but understanding the root of the problem helps in solving it. By using arrow functions, we maintain the correct context of this, preventing common pitfalls.

Next time you face issues with your Angular component's async logic, try this solution and see how it greatly improves your code stability!

If you have any questions or additional tips on handling async calls in Angular, feel free to share your thoughts in the comments!

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