Memongo

Memongo is a lightweight in-memory JSON database with MongoDB-like API and pluggable persistence.

By delegating persistence to user-defined read/write functions, Memongo stays fully environment-agnostic—working out of the box in environments including browsers, Node.js, and WeChat Mini Programs.

✨ Features

• 🧠 In-memory JSON database with MongoDB-like API
• 🔄 Atomic in-memory operations with deferred persistence
• 🔌 Pluggable persistence (Node.js, browser, wechat-miniprogram, custom)
• ⚡ Lightweight and fast
• 🔤 Works in both TypeScript and JavaScript
• 📦 No dependencies

📦 Installation

npm install memongo

🚀 Quick Start

💡 All examples in this repository are written in TypeScript, but they work in JavaScript without any changes.

import { createDatabase } from "memongo";

async function main() {
  // 1) Create an in-memory database (no persistence argument).
  const db = createDatabase();
  await db.init();

  // 2) Create or get a collection.
  let todos = db.collection("todos");
  if (!todos) {
    todos = db.createCollection("todos");
  }

  // 3) Add documents.
  const { _id: buyMilkId } = todos.add({
    title: "Buy milk",
    done: false,
    priority: 2,
  });

  todos.add({
    title: "Read Memongo docs",
    done: false,
    priority: 1,
  });

  console.log("After add:", todos.get());

  // 4) Read one document by id.
  const buyMilk = todos.doc(buyMilkId).get();
  console.log("One doc:", buyMilk);

  // 5) Update one document.
  todos.doc(buyMilkId).update({
    done: true,
  });
  console.log("After doc.update:", todos.get());

  // 6) Remove one document.
  todos.doc(buyMilkId).remove();
  console.log("After doc.remove:", todos.get());

  // 7) Remove all documents in the collection.
  todos.remove();
  console.log("After collection.remove:", todos.get());
}

await main();

⚙️ Persistence Model

Write operations apply changes to the in-memory state synchronously.

If persistence is configured, data is written asynchronously in the background.

To ensure all pending persistence operations are completed, call:

await db.flush();

Persistence-related errors are not thrown during write operations. They are reported when calling flush().

➡️ See this example for detailed usage.

📚 Documentation

👉 Full API documentation

Usage Examples:

• In-memory usage
• Query commands
• Update commands
• Custom persistence (node, browser, wechat-miniprogram)

➡️ See examples

🌍 Environment Support

• ✅ Node.js
• ✅ Browser
• ✅ WeChat Mini Program
• ✅ Any JavaScript runtime (via adapter)

⚠️ Notes

• ESM only → use import
• The package is compiled to ES2022.

🧱 Limitations

• The entire database is rewritten during persistence
• Not suitable for large datasets
• No indexing support yet

🙏 Acknowledgements

Thanks to the following open-source projects:

• MpLocalDB

📄 License

MIT