Bundle Size Monitoring

Problem

JavaScript bundles grow unnoticed until users complain about slow load times. A single dependency addition can balloon bundle size by hundreds of kilobytes, but no one realizes until it’s deployed. Performance degrades gradually with each release as dead code and duplicate dependencies accumulate.

Solution

Integrate bundle analysis into your CI pipeline to measure and compare bundle sizes on every pull request. Set thresholds that fail builds when bundles exceed targets, catching bloat before it reaches production.

Example

This example demonstrates configuring bundle size monitoring that will fail builds if the JavaScript bundle exceeds the defined size threshold.

// package.json - Bundle size monitoring configuration
{
  "scripts": {
    // Add a script to run bundle size analysis
    "analyze": "bundlesize"
  },
  "bundlesize": [
    {
      // Specify which files to check (supports glob patterns)
      "path": "./dist/main.*.js",
      // Set maximum allowed size - build fails if exceeded
      "maxSize": "250 kB"
    }
  ]
}

Benefits

• Catches bundle size regressions before they reach production.
• Makes performance budgets visible and enforceable in the development process.
• Provides immediate feedback on the size impact of dependency additions.
• Prevents gradual performance degradation over time.
• Helps identify and remove duplicate dependencies or dead code.

Tradeoffs

• Requires CI pipeline setup and maintenance for analysis tooling.
• Can slow down CI builds with additional analysis steps.
• May block deployments when size increases are legitimate and necessary.
• Requires team agreement on appropriate thresholds and exceptions.
• Analysis tools may have different methodologies leading to inconsistent results.