bun-macros

Bun Macros

Bun macros run JavaScript at bundle time and inline the results into the output.

Quick Start

// src/config.ts (macro file)
export function getVersion() {
  return "1.0.0";
}

export function getBuildTime() {
  return new Date().toISOString();
}

// src/index.ts (consumer)
import { getVersion, getBuildTime } from "./config" with { type: "macro" };

// At bundle time, these become:
const version = "1.0.0";
const buildTime = "2024-01-15T12:00:00.000Z";

Macro Syntax

// Import with macro attribute
import { fn } from "./macro-file" with { type: "macro" };

// Call the macro (evaluated at build time)
const result = fn();

Common Use Cases

Environment Inlining

// macros/env.ts
export function env(key: string): string {
  return process.env[key] ?? "";
}

// src/index.ts
import { env } from "./macros/env" with { type: "macro" };

const apiUrl = env("API_URL");
// Becomes: const apiUrl = "https://api.example.com";

Git Information

// macros/git.ts
export function gitCommit(): string {
  return Bun.spawnSync(["git", "rev-parse", "HEAD"])
    .stdout.toString().trim();
}

export function gitBranch(): string {
  return Bun.spawnSync(["git", "branch", "--show-current"])
    .stdout.toString().trim();
}

// src/index.ts
import { gitCommit, gitBranch } from "./macros/git" with { type: "macro" };

const BUILD_INFO = {
  commit: gitCommit(),
  branch: gitBranch(),
};
// Inlined at build time

File Embedding

// macros/embed.ts
export function embedFile(path: string): string {
  return Bun.file(path).text();
}

export function embedJSON(path: string): unknown {
  return Bun.file(path).json();
}

// src/index.ts
import { embedFile, embedJSON } from "./macros/embed" with { type: "macro" };

const license = embedFile("./LICENSE");
const config = embedJSON("./config.json");

Build Constants

// macros/constants.ts
export function isDev(): boolean {
  return process.env.NODE_ENV !== "production";
}

export function buildDate(): number {
  return Date.now();
}

export function randomId(): string {
  return Math.random().toString(36).slice(2);
}

// src/index.ts
import { isDev, buildDate, randomId } from "./macros/constants" with { type: "macro" };

if (isDev()) {
  console.log("Development mode");
}

const BUILD_ID = randomId();