Resolving the TypeError: Understanding 'Cannot Call a Class as a Function' in Angular 13

Learn how to fix the `TypeError: Cannot call a class as a function` error in Angular 13 by passing class methods as validator functions correctly.
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Resolving the TypeError: Understanding "Cannot Call a Class as a Function" in Angular 13

If you’re developing an application using Angular 13 and encountering the frustrating error message TypeError: Cannot call a class as a function, you’re not alone. This error often appears during the app's loading phase, despite a successful build process. In this guide, we’ll explore this issue in detail and provide a straightforward solution.

Identifying the Problem

The error arises when attempting to use an Angular class as if it were a function. In Angular's Reactive Forms, validators are expected to be function references. Using a class directly instead of its method can lead to confusion and errors like the TypeError you’re seeing. Here’s a snippet of the error message for context:

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

The error stems from a SpaceValidator class, which is designed to ensure that an input does not contain whitespace. Removing this validator allows the app to function properly, indicating that the validator's implementation needs adjustment.

Understanding the SpaceValidator Class

Here’s the relevant portion of the code that contains the SpaceValidator class:

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

As you can see, the SpaceValidator class contains a method called cannotContainSpace. This method checks if the value of the form control contains a space and returns an error if it does. However, the key issue is using this class method directly in the form control's validators, which leads to the TypeError.

The Solution: Passing Class Methods Correctly

To resolve this error, you need to adjust how the SpaceValidator is referenced in your form configuration. Instead of trying to use the entire class as a validator, access the method directly. Here’s how you can do that:

Correct Syntax

Replace your current validator setup from this:

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

To this:

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

Explanation of Changes

Conclusion

In summary, the TypeError: Cannot call a class as a function error in Angular 13 often occurs when a class is improperly used as a validator. By following the steps outlined above and leveraging the method reference from your class, you can rectify the issue and enhance the robustness of your Angular application.

If you continue to experience issues or need further assistance, feel free to reach out or check additional resources on Angular and Reactive Forms!