Introduction to Promise Memoize

Promise Memoize is a powerful utility library for optimizing JavaScript applications by caching the results of promise-based functions. This can notably enhance the performance of your app by avoiding redundant asynchronous operations.

Key Features and API Examples

1. Basic Usage

To use promise-memoize, you first need to install it:

  npm install promise-memoize

Here’s a simple example of memoizing a promise-based function:

  const memoize = require('promise-memoize');
  const fetchData = async (id) => {
    const response = await fetch(`https://api.example.com/data/${id}`);
    return response.json();
  };
  const memoizedFetchData = memoize(fetchData);

  // Usage
  memoizedFetchData(1).then(data => console.log(data));

2. Custom Cache Key

You can customize the cache key by providing a resolve function:

  const memoizedFetchData = memoize(fetchData, {
    resolve: (id) => `data-${id}`
  });

3. Expiration

Set a cache expiration time to ensure the data is refreshed periodically:

  const memoizedFetchData = memoize(fetchData, {
    maxAge: 60000  // Cache expires in 60 seconds
  });

4. Cache Management

Explicitly clear the cache when needed:

  // Clear all cache
  memoizedFetchData.clear();

  // Clear a specific cache entry
  memoizedFetchData.clear('data-1');

5. Error Handling

Handle errors gracefully within cached functions:

  const fetchDataWithError = async (id) => {
    if (id < 0) throw new Error('Invalid ID');
    const response = await fetch(`https://api.example.com/data/${id}`);
    return response.json();
  };

  const memoizedFetchDataWithError = memoize(fetchDataWithError);

  memoizedFetchDataWithError(-1).catch(err => console.error(err.message));

Application Example

In this example, we will create a simple application that makes API calls to fetch user data. We will utilize promise-memoize to optimize these calls.

  const memoize = require('promise-memoize');

  const fetchUserData = async (userId) => {
    const response = await fetch(`https://api.example.com/user/${userId}`);
    return response.json();
  };

  const memoizedFetchUserData = memoize(fetchUserData, { maxAge: 300000 }); // Cache for 5 minutes

  // Express setup
  const express = require('express');
  const app = express();

  app.get('/user/:id', async (req, res) => {
    try {
      const data = await memoizedFetchUserData(req.params.id);
      res.json(data);
    } catch (err) {
      res.status(500).send(err.message);
    }
  });

  app.listen(3000, () => {
    console.log('Server is running on port 3000');
  });

Using promise-memoize in the above Node.js application ensures that repeated calls to fetch the same user data within 5 minutes will be served from the cache, thereby reducing the number of API requests and enhancing application performance.

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