How to Analyze JavaScript Bundle Size

· Category: Web Performance

Short answer

Analyzing your JavaScript bundle reveals which dependencies contribute the most weight. Smaller bundles parse and execute faster, improving interactivity.

Steps

  1. Install webpack-bundle-analyzer or use the analysis built into Vite.
  2. Run your production build with the analyzer enabled.
  3. Identify large dependencies in the interactive treemap.
  4. Replace heavy libraries with lighter alternatives or tree-shake them.
  5. Split large vendor bundles into separate chunks.

Tips

  • Use import cost extensions in VS Code to see package sizes inline.
  • Check if you are importing the entire library when only one function is needed.
  • Duplicate dependencies often appear when multiple packages require different versions.

Common issues

  • Some analyzers do not show gzip sizes by default; switch to the compressed view.
  • Dynamic imports may appear smaller than they are if not fully loaded during analysis.