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JavaScript
1

Shouldn’t it be transaction.amount? Instead of amount?

https://www.freecodecamp.org/learn/full-stack-developer/lecture-working-with-higher-order-functions-and-callbacks/what-is-method-chaining-and-how-does-it-work

const transactions = [
  { amount: 100, type: "credit" },
  { amount: 20, type: "cash" },
  { amount: 150, type: "credit" },
  { amount: 50, type: "cash" },
  { amount: 75, type: "credit" }
];

const totalCreditWithBonus = transactions
  .filter((transaction) => transaction.type === "credit")
  .map((transaction) => transaction.amount * 1.1)
  .reduce((sum, amount) => sum + amount, 0);

console.log(totalCreditWithBonus); // 357.5

In this line:

.reduce((sum, amount) => sum + amount, 0);

or transaction.amount

2

What does the map() return?

If you changed it to

const totalCreditWithBonus = transactions
  .filter((transaction) => transaction.type === "credit")
  .map((transaction) => transaction.amount * 1.1)

what is returned and stored in totalCreditWithBonus ?

1 Like
3

the array with each amount properly updated to *1.1
but thats not what im talking about

4

But it is exactly what you are talking about. The map method returns an array. The callback in the map methods says the new array is populated with the values transaction.amount * 1.1, which are numbers. Numbers will not have the .amount property.

1 Like
5

oh im sorry i understand now.
so it will create a new array of those values and no objects

6

The map method populates the new array with whatever is returned by the callback.

1 Like