property

BuildOutput.metafile

Metadata about the build:

inputs: every bundled source file with its byte size, imports, and format
outputs: every generated file with its byte size, the inputs that contributed to it, imports between chunks, and exports

Only present when BuildConfig.metafile is true.

Use it for bundle size analysis, inspecting the dependency graph, or as input to bundle analyzer tools.

const result = await Bun.build({
  entrypoints: ['./src/index.ts'],
  outdir: './dist',
  metafile: true,
});

if (result.metafile) {
  // Analyze input files
  for (const [path, input] of Object.entries(result.metafile.inputs)) {
    console.log(`${path}: ${input.bytes} bytes, ${input.imports.length} imports`);
  }

  // Analyze output files
  for (const [path, output] of Object.entries(result.metafile.outputs)) {
    console.log(`${path}: ${output.bytes} bytes`);
    for (const [inputPath, info] of Object.entries(output.inputs)) {
      console.log(`  - ${inputPath}: ${info.bytesInOutput} bytes`);
    }
  }

  // Write to disk for external analysis tools
  await Bun.write('./dist/meta.json', JSON.stringify(result.metafile));
}