Cross-Platform Starter Apps

This repository ships three tiny, runnable "Hello World" apps — one per runtime — in examples/. They are the smallest possible Lesan servers: initialize Lesan, connect to MongoDB, define a model, create an action, and start the server. Each is ~40 lines and shares the exact same logic; only the runner differs.

They live in:

App	Folder	Port	How to run
Node.js	examples/node-app	8080	npm install && npm start
Bun	examples/bun-app	8081	bun install && bun start
Deno	examples/deno-app	8082	deno task start

note

Import from the repo, not npm Because they live inside the Lesan repository, these apps import lesan from the repo source (file:../.. in package.json, "lesan": "../../src/mod.ts" in deno.json) rather than from @hemedani/lesan. In your own project you would use the package: npm install @hemedani/lesan / bun add @hemedani/lesan / jsr:@hemedani/lesan.

The example (same on all three)

import { ActFn, lesan, number, object, string } from "lesan";
import { MongoClient } from "mongodb";

// 1. Initialize Lesan
const app = lesan();

// 2. Connect to MongoDB
const client = await new MongoClient("mongodb://127.0.0.1:27017/").connect();
const db = client.db("lesan_example");
app.odm.setDb(db);

// 3. Define a Model
const userPure = {
  name: string(),
  age: number(),
  email: string(),
};

const users = app.odm.newModel("user", userPure, {});

// 4. Define an Action (Route)
const addUserValidator = () => {
  return object({
    set: object(userPure),
    get: app.schemas.selectStruct("user", 1),
  });
};

const addUser: ActFn = async (body) => {
  const { name, age, email } = body.details.set;
  return await users.insertOne({
    doc: { name, age, email },
    projection: body.details.get,
  });
};

app.acts.setAct({
  schema: "user",
  actName: "addUser",
  validator: addUserValidator(),
  fn: addUser,
});

// 5. Run the Server
app.runServer({
  port: 8080,
  playground: true,
  typeGeneration: true,
});

The five steps are the same five steps as the Getting Started tutorial: lesan() → setDb → newModel → setAct → runServer. The only differences between the apps are the package manager, the MongoDB database name, and the port (8080 / 8081 / 8082) so you can run all three side by side.

Node.js

cd examples/node-app
npm install
npm start      # tsx src/main.ts
npm run dev    # tsx watch src/main.ts (hot reload)

• Runs TypeScript directly with tsx (no build step).
• MongoDB database: lesan_node_example.
• Requires Node.js 18+ and a MongoDB on mongodb://127.0.0.1:27017/.

Bun

cd examples/bun-app
bun install
bun start      # bun run src/main.ts
bun run --watch src/main.ts   # hot reload

• Bun executes TypeScript natively — no transpiler.
• MongoDB database: lesan_bun_example.

Deno

cd examples/deno-app
deno task start    # deno run -A src/main.ts
deno task dev      # deno run -A --watch src/main.ts

• Uses deno.json tasks + an import map ("lesan": "../../src/mod.ts", "mongodb": "npm:mongodb@^6.3.0").
• MongoDB database: lesan_deno_example.

Test any of them

All three expose the same addUser act on POST /lesan (playground enabled):

curl -X POST http://localhost:8080/lesan \
  -H "Content-Type: application/json" \
  -d '{
    "model": "user",
    "act": "addUser",
    "details": {
      "set": { "name": "Ali", "age": 30, "email": "ali@example.com" },
      "get": { "name": 1, "age": 1, "email": 1 }
    }
  }'

Or open the playground at http://localhost:8080/playground (swap the port per runtime).

Why three apps?

These apps prove that a Lesan server is one file regardless of runtime. They are deliberately trivial — the same architecture scales up unchanged to the 15-model Procurement Workflow, which is Deno-based and runs the same framework code.

For the underlying Platform Abstraction Layer and how each runtime's adapter works, see Cross-Platform Support.