Good code / bad code: good code

goodExample.js

function checkoutCart(session) {                                    // this is the code that executes on checkout
  trackActivity(session, ACTIONS.CHECKED_OUT);                      // it tracks that the user is checking out
  return getUserInfo(session.userId)                                // gets the user info with the user id
    .then(user => getDiscountAmount(user))                          // then it gets the discount for the user
    .then(discAmt => addDiscountIfAny(session, discAmt))            // then it applies the discount
    .then(getPaymentScreenConfig)                                   // then it gets the payment screen configuration
    .then(payScrCfg => new PaymentScreen(payScrCfg, session.cart)); // and it returns the payment screen
}

function getDiscountAmount(user) {                                  // this is the code that gets the discount amount
  if (user.hasDiscountedProfile) {                                  // if the user has a profile for discounts
    return retrieveDiscount(user.profileId);                        // it will retrieve that discount
  } else {                                                          // otherwise (user has no discounts)
    return 0;                                                       // discount amount is zero
  }
}

function addDiscountIfAny(session, discAmt) {                       // here we apply discounts if applicable
  if (discAmt > 0) {                                                // if there is a discount amount
    session.cart.addDiscount(discAmt);                              // we add it to the cart
  }
}

the conditional else is not necessary, just

function getDiscountAmount(user) {                                  
  if (user.hasDiscountedProfile) {                                 
    return retrieveDiscount(user.profileId);                  
  }                                                 
  return 0;                                                
}

more short

function getDiscountAmount(user) {   
   return user.hasDiscountedProfile ? retrieveDiscount(user.profileId) : 0;
}