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JavaScript on Miren

Miren auto-detects both Node.js and Bun apps and builds a container image for you — no Dockerfile required. It picks the right package manager from your lockfile and runs the start command from your package.json or Procfile. TypeScript works the same way; either build it during the image build or run it directly with Bun.

Let your agent do this

Ask your AI coding agent to "set up this app on Miren" after installing the Miren agent skills. It detects Node vs. Bun, finds your start script, wires up environment variables, and deploys — using this page as its reference.

Do you need a Dockerfile?​

No. Miren detects your project and builds the image automatically. Provide a Dockerfile.miren only for custom build steps — see Using Dockerfile.miren.

Node.js​

Detection: package.json and a lockfile (package-lock.json or yarn.lock), or a Procfile with a web: node|npm|yarn command. Default version: Node 20.

LockfilePackage managerInstall command
yarn.lockyarnyarn install
package-lock.jsonnpmnpm install

Bun​

Detection: package.json and bun.lock, or a Procfile with a web: bun command. Default version: Bun 1. Bun can run TypeScript directly, so no separate build step is needed for .ts entrypoints.

Set up the app​

From your project root:

miren init
miren deploy

Preview the detected stack, package manager, and start command without building:

miren deploy --analyze

Start command​

Your server must listen on 0.0.0.0 at the port in $PORT — Miren injects PORT and routes traffic to it. Read it in code as process.env.PORT (Node) or Bun.env.PORT / process.env.PORT (Bun). Miren runs your package.json start script by default; a Procfile makes the command explicit:

# Node — direct
web: node server.js

# Node — npm/yarn script
web: npm start

# Next.js
web: npm run start

# Bun — run TypeScript directly
web: bun run src/index.ts

# Bun — Elysia
web: bun run src/server.ts

# Background worker
worker: node worker.js

An Express server, for example, must bind the injected port:

const port = process.env.PORT || 3000;
app.listen(port, "0.0.0.0", () => console.log(`listening on ${port}`));

Building TypeScript / assets​

For Node projects that compile TypeScript or bundle assets, run the build during the image build with an onbuild step in .miren/app.toml:

[build]
onbuild = ["npm run build"]

Then point your start command at the compiled output (e.g. web: node dist/index.js). Bun apps can skip this and run .ts files directly.

See Services to run a worker alongside your web process.

Environment variables​

Set variables with miren env set — -e for plain values, -s for secrets (masked in output and logs):

miren env set -e NODE_ENV=production
miren env set -s DATABASE_URL
miren env set -s SESSION_SECRET

miren env set -s SESSION_SECRET (no value) prompts with masked input. You can also declare variables in .miren/app.toml:

[[env]]
key = "DATABASE_URL"
value = ""
required = true
sensitive = true
description = "Postgres connection string"

See App Configuration — Environment Variables.

Agent quick reference​

  • Detection: package.json + lockfile — bun.lock → Bun, yarn.lock/package-lock.json → Node
  • Default versions: Node 20, Bun 1 (override via [build] version in .miren/app.toml)
  • Install: yarn install / npm install / bun install by lockfile
  • Start command: listen on 0.0.0.0:$PORT via process.env.PORT; runs package.json start by default, or set a Procfile
  • TypeScript: Node → build with [build] onbuild; Bun → runs .ts directly
  • Env vars: miren env set -e KEY=VALUE, -s for secrets, or [[env]] in app.toml
  • Dockerfile: not needed; add Dockerfile.miren only for custom builds

Next steps​