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Encountering `TypeError: o.Subject is not a constructor` after upgrading Angular? Discover how to resolve the issue by upgrading your Angular libraries and ensuring compatibility with RxJS.
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Resolving the TypeError: o.Subject is not a constructor in Angular 11

Upgrading your Angular application can come with its own set of challenges. One common issue developers encounter when transitioning from older versions, such as Angular 5.2 to Angular 11.2, is the error: TypeError: o.Subject is not a constructor. This guide aims to provide a clear breakdown of why this error occurs and how to effectively resolve it.

Understanding the Issue

After you upgrade your Angular version, you may notice that everything works perfectly in development mode, but once you attempt to build your application with Ahead-of-Time (AOT) compilation, the error arises. This can be confusing, especially if no issues appear in development mode.

Key Observations:

Error Context: The error indicates that the Subject constructor from RxJS is not being recognized, which is crucial for managing asynchronous data streams in Angular.

RxJS Version: The RxJS libraries you have in your package.json may not be compatible with the newer Angular version after the upgrade.

Solution: Upgrading Angular Libraries

Step 1: Upgrade Angular CDK and Material

The first step in resolving the TypeError is to ensure that all Angular-related libraries are upgraded to their latest versions. This includes:

@ angular/cdk

@ angular/material

These libraries provide essential components and tools for Angular applications, and if they are running an older version, they may fail to recognize updates in RxJS.

Action Items:

Open your package.json file.

Check the versions for @ angular/cdk and @ angular/material.

Update these libraries to the latest versions that are compatible with Angular 11.

Step 2: Upgrade RxJS Packages

Next, ensure your RxJS packages are also updated. Have a look at your current implementation:

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

Suggested Changes:

Verify you're using the latest rxjs and remove rxjs-compat, as this package is often unnecessary in newer Angular environments.

Run the npm command to update RxJS:

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

Step 3: Rebuild Your Application

After performing the upgrades, it's crucial to rebuild your application. This will allow Angular to apply the changes and resolve any lingering dependencies:

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

If you want to ensure AOT is enabled in your builds, retain the aot option as true in the angular.json file.

Conclusion: Keep It Updated

By ensuring that all libraries are updated and compatible with your Angular version, you can avoid many common errors, such as the TypeError: o.Subject is not a constructor. This not only leads to a smoother development experience but also enhances the overall performance of your application.

Remember, keeping libraries in sync with the Angular version is a best practice that can save you time and headaches in the future. Happy coding!