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Fbuild
Bun

function

build

function build(
config: BuildConfig
): Promise<BuildOutput>;

Bundles JavaScript, TypeScript, CSS, HTML and other supported files into optimized outputs.

@param config

Build configuration options

@returns

Promise that resolves to build output containing generated artifacts and build status

Basic usage - Bundle a single entrypoint and check results

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

if (!result.success) {
  console.error('Build failed:', result.logs);
  process.exit(1);
}

Referenced types

interface BuildConfig

  • banner?: string

    Add a banner to the bundled code such as "use client";

  • bytecode?: boolean

    Generate bytecode for the output. This can dramatically improve cold start times, but will make the final output larger and slightly increase memory usage.

    • CommonJS: works with or without compile: true
    • ESM: requires compile: true

    Without an explicit format, defaults to CommonJS.

    Must be target: "bun"

  • compile?: boolean | CompileTarget | CompileBuildOptions

    Create a standalone executable or self-contained HTML.

    When true, creates an executable for the current platform. When a target string, creates an executable for that platform.

    When used with target: "browser", produces self-contained HTML files with all scripts, styles, and assets inlined. All <script> tags become inline <script> with bundled code, all <link rel="stylesheet"> tags become inline <style> tags, and all asset references become data: URIs. All entrypoints must be HTML files. Cannot be used with splitting.

    // Create executable for current platform
await Bun.build({
  entrypoints: ['./app.js'],
  compile: {
    target: 'linux-x64',
  },
  outfile: './my-app'
});

// Cross-compile for Linux x64
await Bun.build({
  entrypoints: ['./app.js'],
  compile: 'linux-x64',
  outfile: './my-app'
});

// Produce self-contained HTML
await Bun.build({
  entrypoints: ['./index.html'],
  target: 'browser',
  compile: true,
});
  • conditions?: string | string[]

    package.json exports conditions used when resolving imports

    Equivalent to --conditions in bun build or bun run.

    https://nodejs.org/api/packages.html#exports

  • define?: Record<string, string>
  • drop?: string[]

    Drop function calls to matching property accesses.

  • emitDCEAnnotations?: boolean

    Force emitting @PURE annotations even if minify.whitespace is true.

  • entrypoints: string[]

    List of entrypoints, usually file paths

  • env?: 'inline' | 'disable' | `${string}*`

    Controls how environment variables are handled during bundling.

    Can be one of:

    • "inline": Injects environment variables into the bundled output by converting process.env.FOO references to string literals containing the actual environment variable values
    • "disable": Disables environment variable injection entirely
    • A string ending in *: Inlines environment variables that match the given prefix. For example, "MY_PUBLIC_*" will only include env vars starting with "MY_PUBLIC_"
    Bun.build({
  env: "MY_PUBLIC_*",
  entrypoints: ["src/index.ts"],
})
  • external?: string[]
  • features?: string[]

    Enable feature flags for dead-code elimination via import { feature } from "bun:bundle".

    When feature("FLAG_NAME") is called, it returns true if FLAG_NAME is in this array, or false otherwise. This enables static dead-code elimination at bundle time.

    Equivalent to the CLI --feature flag.

    await Bun.build({
  entrypoints: ['./src/index.ts'],
  features: ['FEATURE_A', 'FEATURE_B'],
});
  • files?: Record<string, string | ArrayBufferLike | TypedArray<ArrayBufferLike> | Blob>

    A map of file paths to their contents for in-memory bundling.

    This allows you to bundle virtual files that don't exist on disk, or override the contents of files that do exist on disk. The keys are file paths (which should match how they're imported) and the values are the file contents.

    File contents can be provided as:

    • string - The source code as a string
    • Blob - A Blob containing the source code
    • NodeJS.TypedArray - A typed array (e.g., Uint8Array) containing the source code
    • ArrayBufferLike - An ArrayBuffer containing the source code
    // Bundle entirely from memory (no files on disk needed)
await Bun.build({
  entrypoints: ["/app/index.ts"],
  files: {
    "/app/index.ts": `
      import { helper } from "./helper.ts";
      console.log(helper());
    `,
    "/app/helper.ts": `
      export function helper() {
        return "Hello from memory!";
      }
    `,
  },
});
  • footer?: string

    Add a footer to the bundled code such as a comment block like

    // made with bun!

  • format?: 'esm' | 'cjs' | 'iife'

    Output module format. Top-level await is only supported for "esm".

    Can be:

    • "esm"
    • "cjs" (experimental)
    • "iife" (experimental)
  • ignoreDCEAnnotations?: boolean

    Ignore dead code elimination/tree-shaking annotations such as @PURE and package.json "sideEffects" fields. This should only be used as a temporary workaround for incorrect annotations in libraries.

  • jsx?: { development: boolean; factory: string; fragment: string; importSource: string; runtime: 'classic' | 'automatic'; sideEffects: boolean }

    JSX configuration options

  • loader?: {
    __index[
    key: string
    ]: Loader;
     }
  • metafile?: boolean

    Generate a JSON file containing metadata about the build.

    The metafile contains information about inputs, outputs, imports, and exports which can be used for bundle analysis, visualization, or integration with other tools.

    When true, the metafile JSON string is included in the BuildOutput.metafile property.

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

// Write metafile to disk for analysis
if (result.metafile) {
  await Bun.write('./dist/meta.json', result.metafile);
}

// Parse and analyze the metafile
const meta = JSON.parse(result.metafile!);
console.log('Input files:', Object.keys(meta.inputs));
console.log('Output files:', Object.keys(meta.outputs));
  • minify?: boolean | { identifiers: boolean; keepNames: boolean; syntax: boolean; whitespace: boolean }

    Whether to enable minification.

    Use true/false to enable/disable all minification options. Alternatively, you can pass an object for granular control over certain minifications.

  • naming?: string | { asset: string; chunk: string; entry: string }
  • optimizeImports?: string[]

    List of package names whose barrel files (re-export index files) should be optimized. When a named import comes from one of these packages, only the submodules actually used are parsed — unused re-exports are skipped entirely.

    This is also enabled automatically for any package with "sideEffects": false in its package.json.

    await Bun.build({
  entrypoints: ['./app.ts'],
  optimizeImports: ['antd', '@mui/material', 'lodash-es'],
});
  • outdir?: string
  • packages?: 'external' | 'bundle'
  • publicPath?: string
  • reactFastRefresh?: boolean

    Enable React Fast Refresh transform.

    This adds the necessary code transformations for React Fast Refresh (hot module replacement for React components), but does not emit hot-module code itself.

  • root?: string
  • sourcemap?: boolean | 'linked' | 'external' | 'none' | 'inline'

    Specifies if and how to generate source maps.

    • "none" - No source maps are generated
    • "linked" - A separate *.ext.map file is generated alongside each *.ext file. A //# sourceMappingURL comment is added to the output file to link the two. Requires outdir to be set.
    • "inline" - an inline source map is appended to the output file.
    • "external" - Generate a separate source map file for each input file. No //# sourceMappingURL comment is added to the output file.

    true and false are aliases for "inline" and "none", respectively.

  • splitting?: boolean

    Enable code splitting

  • throw?: boolean
    • When set to true, the returned promise rejects with an AggregateError when a build failure happens.
    • When set to false, returns a BuildOutput with {success: false}
  • tsconfig?: string

    Custom tsconfig.json file path to use for path resolution. Equivalent to --tsconfig-override in the CLI.

    await Bun.build({
  entrypoints: ['./src/index.ts'],
  tsconfig: './custom-tsconfig.json'
});

interface BuildOutput

The output of a build

  • logs: BuildMessage | ResolveMessage[]
  • metafile?: BuildMetafile

    Metadata about the build including inputs, outputs, and their relationships.

    Only present when BuildConfig.metafile is true.

    The metafile contains detailed information about:

    • inputs: All source files that were bundled, their byte sizes, imports, and format
    • outputs: All generated output files, their byte sizes, which inputs contributed to each output, imports between chunks, and exports

    This can be used for:

    • Bundle size analysis and visualization
    • Detecting unused code or dependencies
    • Understanding the dependency graph
    • Integration with 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));
}
  • success: boolean