Lesson 6 - I need some help understanding how and where to use Parameters

[kirkdc]

So I was doing exercise 6 and had a couple of questions which I’ve added in as comments. Any insight into it will be appreciated.

let orderCount = 0;

const takeOrder = (topping, crustType) => {
  orderCount++;
  console.log('Order: ' + crustType + ' pizza topped with ' + topping);
};
//why is itemCount being used as a parameter and why not orderCount?
let getSubTotal = (itemCount) => {
    return itemCount * 7.5;
};
//why orderCount here? i know it gets added everytime takeOrder is called
const getTax = (orderCount) => {
  return getSubTotal(orderCount) *0.06;
};
//why is the parameter left out here
const getTotal = () => {
  return getSubTotal(orderCount) + getTax(orderCount);
};

takeOrder('mushroom', 'thin crust');
takeOrder('spinach', 'whole wheat');
takeOrder('pepperoni', 'brooklyn style');

//when calling a function like getSubTotal below do you have to add its parameter? or does it become an argument when added?
console.log(getSubTotal(orderCount));
console.log(getTotal())

[stetim94]

//why is itemCount being used as a parameter and why not orderCount?
let getSubTotal = (itemCount) => {
return itemCount * 7.5;
};

the parameter has a local scope within the function. Given it the same name as a global variable becomes confusing, how do you know what is what then?

//when calling a function like getSubTotal below do you have to add its parameter? or does it become an argument when added?
console.log(getSubTotal(orderCount));

parameters are placeholders, they get there value from the argument at function call.

//why is the parameter left out here
const getTotal = () => {
return getSubTotal(orderCount) + getTax(orderCount);
};

parameters aren’t mandatory for functions, in this case there is no parameter needed

personally, i disagree with the whole design used here. We both modify and use a global variable and we use it as argument on function calls. I would redesign the whole thing:

const takeOrder = (topping, crustType, currentOrder) => {
  currentOrder++;
  console.log('Order: ' + crustType + ' pizza topped with ' + topping);
  return currentOrder;
};

let getSubTotal = (itemCount) => {
    return itemCount * 7.5;
};

const getTax = (orderCount) => {
  return getSubTotal(orderCount) *0.06;
};

const getTotal = (totalOrders) => {
  return getSubTotal(totalOrders) + getTax(totalOrders);
};

const main = () => {
  let orderCount = 0;
  orderCount = takeOrder('mushroom', 'thin crust', orderCount);
  orderCount = takeOrder('spinach', 'whole wheat', orderCount);
  orderCount = takeOrder('pepperoni', 'brooklyn style', orderCount);
  console.log(getSubTotal(orderCount));
  console.log(getTotal(orderCount))
}
main();

so we don’t have this problem.

[pyplayer52824]

+1 on this:

//why orderCount here? i know it gets added everytime takeOrder is called
const getTax = (orderCount) => {
return getSubTotal(orderCount) *0.06;
};

not giving getTax function any parameter and then just returning getSubTotal(orderCount) * 0.06 seems to work just fine, getting the same final result.

So I’m confused as to why it’s needed there.

[stetim94]

This has always been a problem with this exercise.

Updating global variable is a bad practice:

https://stackoverflow.com/questions/10525582/why-are-global-variables-considered-bad-practice

Why do you think i rewrote the entire program? See my previous reply.

[system]

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