[JS] proxy pattern

class CryptocurrencyAPI {
  getValue(coin) {
    console.log("Calling external API...")

    switch(coin) {
      case "bitcoin": return "$2";
      case "littlecoin": return "$6";
      case "ethernum": return "$9";
    }
  }
}

class cryptocurrencyProxy {
    constructor() {
    this.api = new CryptocurrencyAPI()
    this.cache = {}
  }

  getValue(coin) {
    if (this.cache[coin] == null) {
      this.cache[coin] = this.api.getValue(coin)
    }
    return this.cache[coin]
  }
}

const proxy = new cryptocurrencyProxy()

console.log(proxy.getValue("bitcoin"))
console.log(proxy.getValue("littlecoin"))
console.log(proxy.getValue("ethernum"))
console.log(proxy.getValue("bitcoin"))
console.log(proxy.getValue("bitcoin"))
console.log(proxy.getValue("ethernum"))