Deno & Bun

Node.js has two credible alternatives now, and they exist for different reasons. Deno rewrites the fundamentals — security-by-default, TypeScript without configuration, Web API compatibility, a built-in toolchain. Bun doesn’t change the model; it just makes everything faster. Same npm packages, same package.json, but install times measured in milliseconds and a runtime that benchmarks 2-3× ahead of Node on I/O throughput.

Neither has replaced Node.js in production at scale. But both have found real niches, and Bun as a drop-in package manager alone has earned a permanent place in most developers’ toolbelts.

🟢 Junior

What They Are

Package Management

Deno

deno add hono          # adds to deno.json (uses JSR or npm)
deno add npm:express   # npm packages via npm: prefix

Bun

bun install            # installs from package.json (~25x faster than npm)
bun add express        # add dependency
bun add -d typescript  # dev dependency
bun run dev            # run script from package.json

Bun uses a text-based lockfile (bun.lock, JSONC format) since Bun 1.2. The older binary bun.lockb is still supported but no longer the default.

Running Code

# Deno
deno run app.ts                          # TypeScript, no config needed
deno run --allow-net --allow-read app.ts # explicit permissions required

# Bun
bun run app.ts                           # drop-in for: node app.js
bun app.ts                               # shorthand

🟡 Medior

Deno — Permissions Model

Deno is sandboxed by default — no access to network, filesystem, or env vars unless explicitly granted.

deno run --allow-net --allow-read=./data app.ts

# Granular flags
--allow-net=api.example.com     # restrict to specific host
--allow-env=PORT,DB_URL         # specific env vars only
--allow-write=/tmp              # specific directory only
--allow-all                     # disable sandbox (like Node)

This makes Deno safe for running untrusted third-party scripts.

Deno — Imports & Standard Library

// Modern: deno.json + deno add (uses JSR or npm)
import { Hono } from 'hono'; // after: deno add hono

// npm compatibility (Deno 1.28+)
import express from 'npm:express';

// Standard library (JSR)
import { join }       from '@std/path';
import { assertEquals } from '@std/assert';
import { delay }      from '@std/async';
import { parse }      from '@std/csv';

Deno — Built-in Toolchain

deno fmt      # formatter (replaces Prettier)
deno lint     # linter (replaces ESLint)
deno test     # test runner
deno compile  # compile to a single executable
deno bench    # benchmarking
deno doc      # generate documentation

Bun — Runtime APIs

// Native file API
const file = Bun.file('./data.json');
const data = await file.json();
await Bun.write('./output.txt', 'hello');

// HTTP server (faster than Node's http module)
Bun.serve({
  port: 3000,
  fetch(request) {
    return new Response('Hello from Bun!');
  },
});

Bun — Built-in Test Runner

import { expect, test, describe } from 'bun:test';

describe('UserService', () => {
  test('creates user', async () => {
    const user = await createUser({ email: 'test@test.com' });
    expect(user.id).toBeDefined();
  });
});

bun test            # run all tests
bun test --watch    # watch mode
bun test --coverage # code coverage

Bun — Bundler

await Bun.build({
  entrypoints: ['./src/index.ts'],
  outdir: './dist',
  minify: true,
  target: 'browser', // or 'node' or 'bun'
});

🔴 Senior

Deno vs Bun vs Node.js — Deep Comparison

Runtime performance

• Bun is approximately 3× faster than Node.js on I/O-heavy workloads and cold starts, due to JavaScriptCore’s fast startup and Zig’s low-level memory control.
• bun install is ~25× faster than npm in benchmarks (binary linking, no JS overhead).

Ecosystem & Compatibility

• npm: specifiers were introduced in Deno 1.28, allowing direct npm package imports without a build step.
• Deno 2.0 completed the Node.js compatibility story — adding package.json support, node_modules resolution, and full Node.js API coverage.
• Bun implements the Node.js API (fs, path, http, crypto, stream) at ~95% compatibility, so most Express/Node apps run unchanged: bun run app.js.
• JSR (JavaScript Registry) — Deno’s TypeScript-native alternative to npm; also works in Bun and Node.

Deno Deploy

Serverless edge runtime — deploy TypeScript globally with zero config. Uses the same Web API surface as the browser (no Node.js APIs).

When to Use Each

Senior-Level Points

• Deno’s permission model is the most significant architectural difference — enables running third-party scripts safely without auditing every dependency.
• Bun’s speed comes from JavaScriptCore (fast startup) + Zig’s low-level memory control + bypassing Node abstraction layers.
• Neither fully replaces Node.js — npm ecosystem depth and Node’s decade of production hardening still make it the default for most teams.
• Bun as a package manager only — many teams adopt bun install in existing Node projects without switching the runtime.
• bun install does not execute lifecycle scripts by default — a security-conscious design choice that also speeds up installs.