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Empty Chunks in Angular 19: A Technical Deep Dive

· 5 min read

Recently in our main application built with Angular 19, we encountered a perplexing issue: after deploying to a WebLogic server, certain functionalities on the UI broke completely without any error messages. Below is the technical deep dive into how we diagnosed and resolved the issue, which revolved around unexpected empty chunk files generated during the Angular build process.

Introduction — When the Error First Appeared​

Some of the functionalities on the UI broke completely. There was no console errors or warnings. The angular production build was successful without any errors, yet the deployed frontend failed immediately.

This was specific to Weblogic server. The application worked fine on any other server like Tomcat, websphere etc.

This led us into a detailed debugging journey across build pipelines, server configurations, and module graphs.

Investigating WebLogic Content-Type Issues​

By comparing the working and non working environments, we suspected that it is weblogic which was not setting the Content-Type in case of .js files.

Chrome DevTools has this amazing feature of overriding response headers. We used this feature to set the Content-Type header for .js files to application/javascript on the WebLogic server responses. After reloading the page, everything worked as expected.

So we thought that the issue was with WebLogic not setting correct Content-Type for .js files. We then thought that forcing explicit MIME types to set headers for .js files should work.

However, it did not solve the issue.

The 0-Byte Discovery — Manually Eliminating Suspects​

Further debugging and close observation, we discovered that there was a 0 byte size .js file which was getting downloaded. Once we saw the chunk size was 0 bytes, the suspicion shifted to unused or incorrectly split modules.

We began manual testing:

With Chrome DevTools giving us the option of "Override Content", we could edit the angular generated main.js file from which we removed the import of that 0 byte sized chunk.js file. Running this change, everything worked as expected.

Finding the Root Cause — Using stats.json​

To find out why this 0 byte chunk was created, we generated build statistics:

ng build --configuration production --stats-json

Inside stats.json, we found this entry:

"chunk-F5X5MWHG.js": {
  "imports": [],
  "exports": [],
  "inputs": {
    "node_modules/@angular/material/fesm2022/tooltip.mjs": {
      "bytesInOutput": 0
    }
  },
  "bytes": 0
}

Interpretation​

  • "inputs" indicates the chunk originated from tooltip.mjs
  • "bytesInOutput": 0 means tree-shaking removed all code
  • "bytes": 0 means the emitted chunk is literally empty

This confirmed the root cause:
Unused Angular Material imports can generate empty chunks after tree-shaking.

From stats.json file it was clear that the module from Angular Material — specifically: @angular/material/tooltip — was responsible.

We imported MatTooltipModule but never actually used any tooltip in templates.

Angular’s tree-shaking eliminated the module’s code entirely, yet Webpack still generated a placeholder chunk for it — resulting in a 0-byte JS file, which WebLogic refused to handle cleanly.

Confirming our analysis​

  1. Remove a suspicious import
  2. Rebuild the project
  3. Check whether the empty chunk disappeared

After removing the unused module, angular production build did not generate this empty chunk and everything worked as expected on the weblogic server.

Why This Happens — The Webpack Explanation

Angular CLI uses Webpack under the hood.

Webpack performs:

  • Tree-shaking (eliminating unused code)
  • Module graph evaluation
  • Chunk splitting

According to Webpack documentation:

  • Unused imports are removed entirely
  • But chunk boundaries are determined before tree-shaking
  • Therefore, if an imported module becomes empty, Webpack may still emit an empty chunk file

Sources confirming this behavior:

This is expected behavior in highly optimized builds — but problematic when servers (like WebLogic) cannot handle empty files.

Solution — Eliminating Empty Chunks Safely

There are two main approaches.

1. Remove Unused Imports (Best Fix)​

If you imported:

import { MatTooltipModule } from '@angular/material/tooltip';

…but are not actually using tooltip anywhere:

👉 Remove this import.

This prevents Webpack from generating the chunk entirely.

2. Enable or Enforce removeEmptyChunks​

Webpack has a built-in optimization:

"optimization": {
  "removeEmptyChunks": true
}

Angular CLI enables some of these features internally, but depending on the build graph, empty chunks may still slip through.

This ensures empty chunks are dropped before writing to the output.

Conclusion

The empty chunk issue turned out to be a perfect example of how:

  • Tree-shaking
  • Lazy loading
  • Module splitting
  • Server behavior
  • And unused imports

all intersect in modern frontend pipelines.

Key takeaways:

  • Unused Angular Material imports (like MatTooltipModule) can produce empty chunks
  • stats.json is the fastest way to trace chunk origins
  • Webpack's removeEmptyChunks optimization prevents empty files from being emitted
  • Servers like WebLogic may fail when serving zero-byte JS files

Understanding the underlying build system is essential — because sometimes the issue isn’t in your code or your server, but in the subtle behavior of the bundler connecting the two.