When it comes to storing numbers in MongoDB, you've got two options: Decimal128 and Double. Think of Decimal128 as a ruler for precise measurements and Double as a tape measure for general measurements.

Let's say you're building a stock trading app. You'll want to use Decimal128 for storing the exact price of a stock to ensure accuracy for your users. But for storing the temperature in Celsius in a weather application, Double will be a better option as it's more efficient and doesn't require that level of precision.

Keep in mind, Decimal128 is not a native MongoDB data type, so you'll need to use a library like 'mongodb-decimal' to work with it. Double, however, is native to MongoDB, so no additional libraries are needed.

In short, Decimal128 is like a fancy calculator for precise calculations and Double is like a regular calculator for storing a large range of numbers with less precision. Choose the one that best fits your needs and have fun!

Usage:

Here are a few examples of how to use the Decimal128 data type in MongoDB:

Using the mongodb-decimal library:
You can use the mongodb-decimal library to work with Decimal128 data type in MongoDB.

First, you need to install the library by running the following command:

npm install mongodb-decimal

Then you can use it in your code like this:

const Decimal128 = require('mongodb-decimal');
const decimalValue = new Decimal128("123.45");
// insert into a collection
await collection.insertOne({ value: decimalValue });

// find and update
await collection.updateOne({}, { $set: { value: new Decimal128("999.99") } });

Using the Decimal128 constructor:

const decimalValue = new Decimal128("123.45");

// insert into a collection
await collection.insertOne({ value: decimalValue });

// find and update
await collection.updateOne({}, { $set: { value: new Decimal128("999.99") } });
Using the Decimal128.fromString() method:
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const decimalValue = Decimal128.fromString("123.45");

// insert into a collection
await collection.insertOne({ value: decimalValue });

// find and update
await collection.updateOne({}, { $set: { value: Decimal128.fromString("999.99") } });

In all the examples above, the decimalValue variable holds the Decimal128 value, which can be inserted or updated into a MongoDB collection.

Note that these are just examples and you should make sure to handle any errors and also use the appropriate MongoDB driver version to use Decimal128.