deno-to-bun

Deno to Bun Migration

You are assisting with migrating an existing Deno project to Bun. This involves converting Deno APIs, updating configurations, and adapting to Bun's runtime model.

Quick Reference

For detailed patterns, see:

• API Mapping: api-mapping.md - Deno.* to Bun equivalents
• Permissions: permissions.md - Permission model differences

Migration Workflow

1. Pre-Migration Analysis

Check if Bun is installed:

bun --version

Analyze current Deno project:

# Check Deno version
deno --version

# Check for deno.json/deno.jsonc
ls -la | grep -E "deno.json|deno.jsonc"

# List permissions used
grep -r "deno run" .

Read deno.json or deno.jsonc to understand the project configuration.

2. API Compatibility Analysis

Common Deno APIs and their Bun equivalents:

File System

// Deno
const text = await Deno.readTextFile("file.txt");
await Deno.writeTextFile("file.txt", "content");

// Bun
const text = await Bun.file("file.txt").text();
await Bun.write("file.txt", "content");

HTTP Server

// Deno
Deno.serve({ port: 3000 }, (req) => {
  return new Response("Hello");
});

// Bun
Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response("Hello");
  },
});

Environment Variables

// Deno
const value = Deno.env.get("KEY");

// Bun (same as Node.js)
const value = process.env.KEY;

Reading JSON

// Deno
const data = await Deno.readTextFile("data.json");
const json = JSON.parse(data);

// Bun
const json = await Bun.file("data.json").json();

For complete API mapping, see api-mapping.md.

3. Configuration Migration

Convert deno.json to package.json and bunfig.toml:

deno.json:

{
  "tasks": {
    "dev": "deno run --allow-net --allow-read main.ts",
    "test": "deno test"
  },
  "imports": {
    "oak": "https://deno.land/x/[email protected]/mod.ts"
  },
  "compilerOptions": {
    "lib": ["deno.window"]
  }
}