How to Bundle TypeScript Declarations and JavaScript Files Together with Rollup

Learn how to correctly compile TypeScript declarations and JavaScript files together in Rollup to solve common integration issues.
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Understanding the Problem: Bundling TypeScript and JavaScript Files Separately

When using Rollup to compile a project with TypeScript and JavaScript files, you may encounter a frustrating problem: the TypeScript declaration files and JavaScript files get bundled separately. This can lead to errors when importing the files in another repository, where the system fails to recognize the declaration files.

When trying to import your packaged library, you might run into an error similar to this:

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

Digging Deeper: The Rollup Configuration

Let's dive into a typical Rollup configuration file that could lead to the aforementioned issue. Here’s an example configuration:

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

While this configuration seems fair, the external field defines packages that should not be bundled. Failing to include all the necessary external dependencies can lead to the creation of a lib/node_modules folder, which complicates the output structure further.

Output Structure Example

In its problematic form, the output structure appears as follows:

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

This output structure generates confusion and potential runtime errors when trying to utilize the package in another project.

The Solution: Correctly Configure External Dependencies

To resolve the issue, you need to ensure that all relevant external dependencies are correctly declared in the Rollup configuration. Here's how to modify it:

Add Missing Packages: Include all packages that your files depend on within the external array of the Rollup config.

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

By explicitly defining every external package your code utilizes, Rollup no longer attempts to bundle them, ensuring that the TypeScript declarations and JavaScript files are bundled together appropriately.

Final Output Structure

When configured correctly, your output structure will look more organized:

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

Conclusion

Properly setting up Rollup to compile your TypeScript declarations and JavaScript files together is crucial for smooth integration in other projects. Remember to include all necessary packages in the external configuration to avoid any mismatched errors.

If you encounter issues along the way, don’t hesitate to verify your dependencies. Often, the problem resides in overlooked configurations or missing external dependencies.

By keeping these points in mind, you can ensure your Rollup build process runs seamlessly, eliminating common pitfalls along the way.