Promises for asynchronous programming – Exercise

Hi, here an exercise that is resolved with Javascript promises.

// Eventually resolves w/ an array of coupons (array of strings)
// this function will return the resolve response like ["coupon1", "coupon3", "coupon2"]
function getCoupons() {
    return new Promise((resolve) => {
        setTimeout(() => resolve(['coupon1','coupon3', 'coupon2', ]), Math.random() * 10);
    });
}

// Eventually resolves w/ a discount (number)
// This method will read each item of the array ["coupon1", "coupon3", "coupon2"]
async function tryCoupon(coupon = '') {

    // Will return a promise
    return new Promise((resolve) => {
      // variable to save the discount
      let discount = 0;

      // Depend of the text of the item then will return
      // the value of that coupon
      switch(coupon) {
        case 'coupon1':
          discount = 80; break;
        case 'coupon2':
          discount = 20; break;
        case 'coupon3':
          discount = 30; break;
      }

      // Then we will return the response (Resolve) after setTimeout time
      setTimeout(() => resolve(discount), Math.random() * 10);
    });
}

async function getBestCoupon() {
    // Wait until getCoupons is resolve
    // This const will have the data ["coupon1", "coupon3", "coupon2"]
    const couponsResult =  await getCoupons();

    // Variables to save largestDiscount and largestCoupon
    let largestDiscount = 0;
    let largestCoupon = '';

    // Then go through every position in the resolve data
    for (var i=0; i < couponsResult.length; i++) {
      // Is each item in the array like -> coupon1, coupon2, coupon3
      const couponEach = couponsResult[i];

      // For every item in the array we will run the tryCoupon Method
      // The method will return us the value of each item 
      // like -> 80, 30, 20
      const resultEach = await tryCoupon(couponEach);

      // Will comparing to get the largest coupon
      if (resultEach > largestDiscount) {
        largestDiscount = resultEach;
        largestCoupon = couponEach
      }
    }

    console.log('The largest coupon is -->', largestCoupon);
    
    // Finally will return the largest coupon
    return largestCoupon;
}

 getBestCoupon().then(console.log)

Result:

By Cristina Rojas.