Bun CLI tree-shaking always enabled
Tree-shaking is always true in Bun's bundler. The esbuild `--tree-shaking` flag is not applicable.
cli
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Bun version command
To see the version of Bun, run `bun --version`. The esbuild `--version` flag for the bundler is not applicable.
Bun CLI --drop flag supported
Bun CLI supports the `--drop` flag, same as esbuild.
Bun CLI --tsconfig-override replaces esbuild --tsconfig
Bun uses `--tsconfig-override` instead of esbuild's `--tsconfig`.
Bun CLI --root replaces esbuild --outbase
Bun uses `--root` instead of esbuild's `--outbase`.
Bun CLI --public-path supported
Bun CLI supports the `--public-path` flag, same as esbuild.
CLI syntax for bun build vs esbuild
The basic CLI syntax differs: esbuild uses `esbuild <entrypoint> --outdir=out --bundle` while Bun uses `bun build <entrypoint> --outdir=out`. Boolean flags like `--minify` take no argument in Bun. Flags that take a value, like `--outdir <path>`, can be written as `--outdir out` or `--outdir=out`. Some flags, like `--define`, can be repeated: `--define foo=bar --define bar=baz`.
Bun CLI --no-bundle flag
In Bun CLI, use `--no-bundle` to disable bundling. Bun always bundles by default, unlike esbuild which requires `--bundle`.
Bun CLI --define flag syntax
Bun's `--define` flag uses `--define K=V` syntax without a colon, whereas esbuild uses `--define:K=V`. Example: `bun build --define foo=bar` instead of `esbuild --define:foo=bar`.
Bun CLI --external flag syntax
Bun's `--external` flag uses `--external <pkg>` syntax without a colon, whereas esbuild uses `--external:<pkg>`. Example: `bun build --external react` instead of `esbuild --external:react`.
Bun CLI --format values
Bun supports format values of `"esm"`, `"cjs"`, and `"iife"`. esbuild defaults to `"iife"`, but Bun does not specify a stated default.
Bun CLI --loader flag syntax and supported loaders
Bun's `--loader` flag syntax is `--loader .ext:loader` (e.g., `bun build app.ts --loader .svg:text`), whereas esbuild uses `--loader:.ext=loader` (e.g., `esbuild app.ts --bundle --loader:.svg=text`). Bun supports a different set of built-in loaders than esbuild. The esbuild loaders `dataurl`, `binary`, `base64`, `copy`, and `empty` are not implemented in Bun.
Bun CLI --target replaces esbuild --platform
In Bun CLI, `--target` is used instead of esbuild's `--platform`, renamed for consistency with tsconfig. Bun's `--target` does not support `neutral`.
Bun CLI --asset-naming replaces esbuild --asset-names
Bun uses `--asset-naming` instead of esbuild's `--asset-names`, renamed for consistency with naming in the JS API.
Bun CLI --banner and --footer only apply to JS bundles
In Bun CLI, `--banner` and `--footer` flags only apply to JavaScript bundles, not CSS or other asset types.
Bun CLI --chunk-naming replaces esbuild --chunk-names
Bun uses `--chunk-naming` instead of esbuild's `--chunk-names`, renamed for consistency with naming in the JS API.
Bun CLI --color always enabled
In Bun CLI, color output is always enabled. The esbuild `--color` flag is not applicable.
Bun CLI --feature flag for compile-time dead-code elimination
Bun-specific `--feature` flag enables feature flags for compile-time dead-code elimination through `import { feature } from "bun:bundle"`.
Bun CLI --entry-naming replaces esbuild --entry-names
Bun uses `--entry-naming` instead of esbuild's `--entry-names`, renamed for consistency with naming in the JS API.
Bun CLI --ignore-dce-annotations replaces esbuild --ignore-annotations
Bun uses `--ignore-dce-annotations` instead of esbuild's `--ignore-annotations`.
Bun CLI --jsx-runtime replaces esbuild --jsx
Bun uses `--jsx-runtime <runtime>` instead of esbuild's `--jsx`. Supports `"automatic"` (uses jsx transform) and `"classic"` (uses `React.createElement`).
Bun CLI JSX default handling from tsconfig.json
Bun reads `compilerOptions.jsx` from `tsconfig.json` to determine a default. If `compilerOptions.jsx` is `"react-jsx"`, or if `NODE_ENV=production`, Bun uses the jsx transform. Otherwise, it uses `jsxDEV`. The bundler does not support `preserve`.
Bun CLI --jsx-factory, --jsx-fragment, --jsx-import-source supported
Bun CLI supports `--jsx-factory`, `--jsx-fragment`, and `--jsx-import-source` flags, same as esbuild.
Bun CLI --keep-names supported
Bun CLI supports the `--keep-names` flag, same as esbuild.
Bun CLI --metafile supported
Bun CLI supports the `--metafile` flag, same as esbuild.
Bun CLI minification granular flags
Bun CLI supports `--minify-whitespace`, `--minify-identifiers`, and `--minify-syntax` flags for granular control over minification, same as esbuild.
Running dev server with HTML file
To start the development server, run `bun ./index.html`. The server provides automatic bundling, multi-entry support, TypeScript and JSX support, CSS bundling and minification, and asset management with path rewriting.
Multi-page app (MPA) multiple entry points
To support multiple HTML entry points, pass them all to `bun`: `bun ./index.html ./about.html`. This serves index.html at / and about.html at /about.
Glob patterns for HTML entry points
You can use glob patterns ending in .html to specify multiple HTML files: `bun ./**/*.html`. Bun will discover all matching HTML files and serve them as separate routes.
Environment variable inlining in production build CLI
When building for production with `bun build`, use the --env flag to inline environment variables: `bun build ./index.html --outdir=dist --env=inline` to inline all environment variables, or `bun build ./index.html --outdir=dist --env=PUBLIC_*` to only inline vars with a specific prefix (recommended).
Browser console logs to terminal with --console flag
Bun's dev server can stream console logs from the browser to the terminal by passing the --console CLI flag: `bun ./index.html --console`. Each call to console.log or console.error is broadcast to the terminal, so browser errors show up where you run the server. Internally, this reuses the WebSocket connection from hot module replacement (HMR).
Dev server keyboard shortcuts
While the dev server is running: `o + Enter` opens in browser, `c + Enter` clears console, `q + Enter` or `Ctrl+C` quits the server.
Production build with bun build command
Use `bun build ./index.html --minify --outdir=dist` to create optimized production bundles.
Watch mode with bun build --watch
Run `bun build --watch` to watch for changes and rebuild automatically. This works well for library development.
bun build CLI basic syntax
The CLI command to bundle code is: `bun build <entry> --outdir ./out`. Multiple entrypoints can be provided as separate arguments.
Watch mode for incremental rebuilds
Watch mode is enabled with --watch flag: `bun build ./index.tsx --outdir ./out --watch`. Supports incremental rebuilds like the runtime and test runner.
--minify CLI flag
The --minify flag enables all minification modes: whitespace minification, syntax minification, and identifier minification. Usage: bun build ./index.ts --minify --outfile=out.js
--production CLI flag enables minification
The --production flag automatically enables minification and also sets process.env.NODE_ENV to production and enables the production-mode JSX import & transform. Usage: bun build ./index.ts --production --outfile=out.js
--minify-whitespace CLI flag
The --minify-whitespace flag removes all unnecessary whitespace, newlines, and formatting from the output. Usage: bun build ./index.ts --minify-whitespace --outfile=out.js
--minify-syntax CLI flag
The --minify-syntax flag rewrites JavaScript syntax to shorter equivalent forms and performs constant folding, dead code elimination, and other optimizations. Usage: bun build ./index.ts --minify-syntax --outfile=out.js
--minify-identifiers CLI flag
The --minify-identifiers flag renames local variables and function names to shorter identifiers using frequency-based optimization. Usage: bun build ./index.ts --minify-identifiers --outfile=out.js
--drop=debugger CLI flag
The --drop=debugger flag removes debugger statements from code during minification.
--drop=console CLI flag
The --drop=console flag removes all console.* method calls from code during minification. Calls are replaced with void 0.
--drop=<name> CLI flag
The --drop=<name> flag removes calls to specified global functions and their methods. Example: --drop=assert removes all assert() and assert.* calls.
--keep-names flag for minification
The --keep-names flag preserves the .name property on functions and classes while still minifying the identifiers themselves. Useful for debugging. Usage: bun build ./index.ts --minify --keep-names --outfile=out.js