Solving TypeError: Cannot read properties of undefined (reading 'page') in Angular Pagination

Описание: Discover a step-by-step solution to the `TypeError: Cannot read properties of undefined (reading 'page')` issue with Angular server-side pagination. Learn how to effectively fix this common problem!
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Solving TypeError: Cannot read properties of undefined (reading 'page') in Angular Pagination

If you're working with Angular and implementing server-side pagination, you may encounter the frustrating error:

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

This issue often arises in the context of mat-paginator, where the paginator component tries to access properties before they are ready, especially when using the async pipe. In this guide, we will walk through the problem, identify the root cause, and illustrate an effective solution.

Understanding the Problem

In the provided scenario, you have an Angular component that manages a list of services with pagination. When attempting to interact with the paginator, the application throws the error indicating that it cannot access the page property, meaning that it is attempting to perform an action on an undefined object.

Why Does This Error Occur?

This error generally arises due to the structure of your HTML, where:

The mat-paginator is nested within an <ng-container> that only exists if the listings$ observable is ready and fully resolved.

If the observable has not emitted a value (i.e., the data is not yet available), the paginator does not exist on the page, leading the code to try accessing properties on undefined.

The Solution

The solution to this error is simple yet effective: move the mat-paginator outside the ng-container. This means that the paginator component will always be present in the DOM, allowing it to interact properly even when the data is still loading.

Step-by-Step Instructions

Here's how to implement the solution:

Identify the HTML Structure: Locate the mat-paginator declaration within your HTML template.

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

Move the Paginator: Transfer the mat-paginator outside of the ng-container.

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

Test Your Changes: Refresh your application and ensure that the paginator works as expected without throwing the TypeError.

Conclusion

The TypeError: Cannot read properties of undefined (reading 'page') in Angular pagination can be a common stumbling block, especially for those new to async operations. By appropriately placing your mat-paginator outside of any conditions that depend on asynchronous data, you can avoid these errors and create a smoother user experience.

Implementing this simple structural change will enhance your Angular application, ensuring that you harness the full power of server-side pagination without errors. Don't hesitate to reach out if you require further assistance or clarification!