Introduction to promise-memoize

promise-memoize is a powerful memoization library tailored specifically for handling promises in JavaScript. By caching the results of promise-returning functions, it helps in significantly improving performance and avoiding unnecessary re-executions. This is particularly useful in scenarios involving repetitive and costly asynchronous operations.

Why Use promise-memoize?

Memoization is a key optimization technique that stores the results of expensive function calls and returns the cached result when the same inputs occur again. promise-memoize extends this concept to promises, enhancing the efficiency of asynchronous operations.

Getting Started

To use promise-memoize, install it via npm:

npm install promise-memoize

Here’s a basic example to help you get started:

const memoize = require('promise-memoize');
async function fetchData() {
 // Simulate a data fetching operation
 return new Promise(resolve => setTimeout(() => resolve('data'), 1000));
}
const memoizedFetchData = memoize(fetchData);
memoizedFetchData().then(console.log);  // Fetches data and caches it memoizedFetchData().then(console.log);  // Returns cached data 

API Examples

Basic Usage

const memoizedFunc = memoize(asyncFunction, { maxAge: 5000 });
memoizedFunc('arg1').then(console.log); memoizedFunc('arg1').then(console.log);  // Cached result returned if within 5 seconds 

Handling Multiple Arguments

const memoizedFunc = memoize(multiArgFunction, { primitive: true });
memoizedFunc('arg1', 'arg2').then(console.log); memoizedFunc('arg1', 'arg2').then(console.log);  // Cached result for the arguments combination 

Custom Cache Key Generation

const memoizedFunc = memoize(asyncFunction, {
 resolve: (arg1, arg2) => `${arg1}-${arg2}`
});
memoizedFunc('arg1', 'arg2').then(console.log); memoizedFunc('arg1', 'arg2').then(console.log);  // Custom key-based caching 

Example Application

Let’s illustrate how you can use promise-memoize in a real-world application:

const express = require('express'); const fetch = require('node-fetch'); const memoize = require('promise-memoize');
const app = express(); const port = 3000;
async function getUserData(id) {
 const response = await fetch(`https://jsonplaceholder.typicode.com/users/${id}`);
 const data = await response.json();
 return data;
}
const memoizedGetUserData = memoize(getUserData, { maxAge: 60000 });
app.get('/user/:id', async (req, res) => {
 const id = req.params.id;
 try {
   const data = await memoizedGetUserData(id);
   res.json(data);
 } catch (error) {
   res.status(500).send(error.toString());
 }
});
app.listen(port, () => {
  console.log(`Server running at http://localhost:${port}`);
}); 

This Express.js application demonstrates how to cache API responses to improve performance significantly, especially on endpoints with high traffic.

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