Memoized Async Function

index.js

import axios from 'axios'

class App {
  constructor() {
    this.cache = {}
  }

  /**
   * 何もキャッシュしないバージョン
   */
  async request1(url) {
    return await axios.get(url)
  }

  /**
   * API の結果をキャッシュするバージョン
   */
  async request2(url) {
    if (!this.cache[url]) {
      this.cache[url] = await axios.get(url)
    }
    return this.cache[url]
  }

  /**
   * Promise をキャッシュするバージョン
   */
  async request3(url) {
    if (!this.cache[url]) {
      this.cache[url] = axios.get(url)
    }
    return this.cache[url]
  }

  /**
   * API を使って何かするメソッド
   */
  async doSomethingWithAPI(url, index) {
    const result = await this.request3(url)
    console.log(index, result.data)
  }

  async main() {
    const url = 'http://localhost:8000/api/test.json'
    for (let i = 0; i < 10; i++) {
      await this.sleep(1)
      this.doSomethingWithAPI(url, i)
    }
  }

  async sleep(msec) {
    return new Promise(resolve => setTimeout(resolve, msec))
  }
}

const app = new App()
app.main()

package.json

{
  "name": "memoized-async-function",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "type": "module",
  "dependencies": {
    "axios": "^0.21.1"
  },

  "scripts": {
    "start": "node index.js",
    "server": "node server.js"
  }
}

server.js

import http from 'http'

const port = 8000

let count = 0
http.createServer(async (req, res) => {
  // 少しタイミングを遅らせるため、console.log() を出力します。
  console.log(new Date(), req.url)

  count += 1
  res.writeHead(200, {'Content-Type': 'application/json'})
  res.write(`{"count": ${count}}`)
  res.end()
}).listen(port)

console.log(`Server running at http://localhost:${port}`)