unplugin-macros

Macros are a mechanism for running JavaScript functions at bundle-time. The value returned from these functions or variables are directly inlined into your bundle.

Installation

# npm
npm i -D unplugin-macros

# jsr
npx jsr add -D @unplugin/macros

Vite

// vite.config.ts
import Macros from 'unplugin-macros/vite'

export default defineConfig({
  plugins: [Macros()],
})

Rollup

// rollup.config.js
import Macros from 'unplugin-macros/rollup'

export default {
  plugins: [Macros()],
}

esbuild

Requires esbuild >= 0.15

// esbuild.config.js
import { build } from 'esbuild'

build({
  plugins: [require('unplugin-macros/esbuild')()],
})

Webpack

// webpack.config.js
module.exports = {
  /* ... */
  plugins: [require('unplugin-macros/webpack')()],
}

Usage

// main.js
import { buildTime, getRandom } from './macros.js' with { type: 'macro' }

getRandom() // Will be replaced with a random number at build time
buildTime // Will be replaced with the timestamp at the build time

// macros.js
export function getRandom() {
  return Math.random()
}
export const buildTime = Date.now()

Macro specifiers are resolved by the runner. The default runner follows Node.js' ESM resolution, so relative specifiers need their file extension — './macros.js', not './macros'.

Function Arguments

You can pass function values as arguments to macros. Functions must be isolated (no references to outside identifiers):

// main.js
import { transform } from './macros.js' with { type: 'macro' }

transform(() => 42)
transform(async () => {
  const os = await import('node:os')
  return os.endianness()
})

See more in Bun Macros.

MacroContext

Every macro is invoked with a MacroContext as its this. The most useful fields are:

Field	Description
id	Absolute path of the file being transformed.
source	Full source code of the file.
ast.call	CallExpression AST node of this macro invocation (await / tagged template are unwrapped).
ast.program	Program AST of the whole file.
emitFile	Emit additional bundle assets.
unpluginContext	The underlying unplugin build context — experimental, may change.

ast.call carries the source offsets (start, end) of the invocation, which is enough to build callsite-aware macros without paying for a runtime stack walk:

// macros.ts
import path from 'node:path'
import type { MacroContext } from 'unplugin-macros'

export function $callsite(this: MacroContext): string {
  const before = this.source.slice(0, this.ast.call.start)
  const line = before.split('\n').length
  const column = this.ast.call.start - (before.lastIndexOf('\n') + 1)
  return `${path.basename(this.id)}:${line}:${column}`
}

// main.ts
import { $callsite } from './macros.ts' with { type: 'macro' }

console.log($callsite()) // → 'main.ts:3:12'

TypeScript

Import Attributes syntax is supported in TypeScript 5.3 and above.

ESLint

Import Attributes syntax is supported in ESLint v9.14.0.

Runners

A runner resolves and executes macro modules. Two are built in, and both resolve macro specifiers the same way — following Node.js' ESM resolution, so relative specifiers need their file extension ('./macros.ts', not './macros').

Editing a macro module — or anything it imports — invalidates it during dev.

nativeRunner (default)

Runs macros on Node.js' native ESM loader. Nothing is bundled or transpiled ahead of time, which makes it the cheapest option, and it needs no extra dependency.

TypeScript relies on Node's native type stripping, so:

• non-erasable syntax (enum, namespace, parameter properties) is not supported
• macro modules published as .ts inside node_modules cannot be loaded
• no aliases, tsconfig paths, JSX, or non-JS imports inside macro modules

import { nativeRunner } from 'unplugin-macros'
import Macros from 'unplugin-macros/vite'

Macros({ runner: nativeRunner() })

unrunRunner

Bundles each macro module with unrun (Rolldown) before executing it, so everything Rolldown understands works: enum and other non-erasable TypeScript syntax, JSX, extensionless imports inside the macro module, tsconfig paths, and aliases or plugins via inputOptions.

Requires unrun to be installed — it is an optional peer dependency.

import { unrunRunner } from 'unplugin-macros'
import Macros from 'unplugin-macros/vite'

Macros({
  runner: unrunRunner({
    inputOptions: { resolve: { alias: { '~': './src' } } },
  }),
})

Custom runners

Any object matching the MacroRunner interface works — this is the escape hatch for loaders such as jiti or tsx:

import path from 'node:path'
import { createJiti } from 'jiti'
import Macros from 'unplugin-macros/vite'

const jiti = createJiti(import.meta.url)

Macros({
  runner: {
    resolve: (source, importer) =>
      jiti.esmResolve(source, { parentURL: path.dirname(importer) }),
    import: (resolved) => jiti.import(resolved),
  },
})

init (called once, lazily, only when a macro is actually found), invalidate and close are optional.

Options

Refer to docs.

Thanks

Thanks to Bun Macros.

Sponsors

License

MIT License © 2023-PRESENT Kevin Deng