memongo

memongo is a lightweight, ZERO-dependency, in-memory document database with pluggable persistence.

Features

• No dependencies – Zero bloat, zero install friction.
• Pluggable persistence – Drop in any adapter and run anywhere.
• Atomic operations – Safe, batchable updates.
• Lightweight and fast – Synchronous, in-memory performance.
• Full TypeScript support – Types built right in.

Installation

npm install memongo
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Quick Start

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

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: drinkMilkId } = todos.add({
    title: "Drink milk in the morning",
    done: false,
    priority: 0,
  });

  todos.add({
    title: "Eat snacks in the afternoon",
    done: false,
    priority: 2,
  });

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

  todos.add({
    title: "Use memongo in my project and add learning tests",
    done: false,
    priority: 1,
  });

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

  // 4) Get single document.
  const drinkMilk = todos.doc(drinkMilkId).get();
  console.log("\nThe Drink milk todo:", drinkMilk);

  // 5) Update single document.
  todos.doc(drinkMilkId).update({
    done: true,
  });
  console.log("\nAfter marking drink milk as done:", todos.get());

  // 6) Get documents that satisfy the condition.
  const doneTodos = todos.where({ done: true }).get();
  console.log("\nDone todos:", doneTodos);

  // 7) Remove single document.
  todos.doc(drinkMilkId).remove();
  console.log("\nAfter removing the done Drink milk todo:", todos.get());

  // 8) Update documents that satisfy the condition.
  todos.where({ done: false, priority: 1 }).update({ done: true });
  console.log("\nAfter marking todos with priority 1 as done:", todos.get());

  // 9) Remove documents that satisfy the condition.
  todos.where({ done: true }).remove();
  console.log("\nAfter removing done todos:", todos.get());

  // 10) Remove all documents in the collection.
  todos.remove();
  console.log("\nAfter clearing the todo collection:", todos.get());
}

main();
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Persistence Model

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

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

To ensure all pending persistence operations are completed (which is usually not needed), call:

await db.flush();
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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 (including basic CRUD usage)
• Query commands
• Update commands
• Custom persistence (node, browser, wechat-miniprogram)

See examples

Notes

• ESM only → use import
• Not suitable for large datasets (>=10MB)

Acknowledgements

Thanks to the following open-source projects:

• MpLocalDB

License

MIT