Shows how ES "classes" are really just functions

class_vs_fn.js

class Stripe {
  constructor(baseUrl, token) {
    this.baseUrl = baseUrl;
    this.token = token;
    this.expensiveResult = null;
  }
  getCustomers() {
    console.log(`Getting ${this.baseUrl}/customers with token ${this.token}`);
  }
  someExpensiveOperation() {
    return new Promise((resolve, _) => {
        if (this.expensiveResult) {
          resolve(this.expensiveResult);
        } else {
          setTimeout(() => {
            this.expensiveResult = 10;
            resolve(10);
          }, 1000);
        }
      });
  }
}

console.log("Class based:");
const stripe = new Stripe("https://api.stripe.com/v1", "xyz");
stripe.getCustomers("/customers");
stripe.someExpensiveOperation().then(x => console.log(x));
stripe.someExpensiveOperation().then(x => console.log(x));
stripe.someExpensiveOperation().then(x => console.log(x));

function Stripe2(baseUrl, token) {
  let expensiveResult = null;
  return {
    getCustomers: () => console.log(`Getting ${baseUrl}/customers with token ${token}`),
    someExpensiveOperation: () => {
      return new Promise((resolve, _) => {
        if (expensiveResult) {
          resolve(expensiveResult);
        } else {
          setTimeout(() => {
            expensiveResult = 10;
            resolve(10);
          }, 1000);
        }
      });
    }
  }

}

console.log("Function based:");
const {getCustomers, someExpensiveOperation} = Stripe2("https://api.stripe.com/v1", "xyz");
getCustomers();
someExpensiveOperation().then(x => console.log(x));
someExpensiveOperation().then(x => console.log(x));
someExpensiveOperation().then(x => console.log(x));