freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/understand-functional-programming-terminology.md

---
id: 587d7b8e367417b2b2512b5c
title: Understand Functional Programming Terminology
challengeType: 1
forumTopicId: 301240
dashedName: understand-functional-programming-terminology
---

# --description--

The FCC Team had a mood swing and now wants two types of tea: green tea and black tea. General Fact: Client mood swings are pretty common.

With that information, we'll need to revisit the `getTea` function from last challenge to handle various tea requests. We can modify `getTea` to accept a function as a parameter to be able to change the type of tea it prepares. This makes `getTea` more flexible, and gives the programmer more control when client requests change.

But first, let's cover some functional terminology:

<dfn>Callbacks</dfn> are the functions that are slipped or passed into another function to decide the invocation of that function. You may have seen them passed to other methods, for example in `filter`, the callback function tells JavaScript the criteria for how to filter an array.

Functions that can be assigned to a variable, passed into another function, or returned from another function just like any other normal value, are called <dfn>first class</dfn> functions. In JavaScript, all functions are first class functions.

The functions that take a function as an argument, or return a function as a return value are called <dfn>higher order</dfn> functions.

When functions are passed in to or returned from another function, then those functions which were passed in or returned can be called a <dfn>lambda</dfn>.

# --instructions--

Prepare 27 cups of green tea and 13 cups of black tea and store them in `tea4GreenTeamFCC` and `tea4BlackTeamFCC` variables, respectively. Note that the `getTea` function has been modified so it now takes a function as the first argument.

Note: The data (the number of cups of tea) is supplied as the last argument. We'll discuss this more in later lessons.

# --hints--

The `tea4GreenTeamFCC` variable should hold 27 cups of green tea for the team.

```js
assert(tea4GreenTeamFCC.length === 27);
```

The `tea4GreenTeamFCC` variable should hold cups of green tea.

```js
assert(tea4GreenTeamFCC[0] === 'greenTea');
```

The `tea4BlackTeamFCC` variable should hold 13 cups of black tea.

```js
assert(tea4BlackTeamFCC.length === 13);
```

The `tea4BlackTeamFCC` variable should hold cups of black tea.

```js
assert(tea4BlackTeamFCC[0] === 'blackTea');
```

# --seed--

## --seed-contents--

```js
// Function that returns a string representing a cup of green tea
const prepareGreenTea = () => 'greenTea';

// Function that returns a string representing a cup of black tea
const prepareBlackTea = () => 'blackTea';

/*
Given a function (representing the tea type) and number of cups needed, the
following function returns an array of strings (each representing a cup of
a specific type of tea).
*/
const getTea = (prepareTea, numOfCups) => {
  const teaCups = [];

  for(let cups = 1; cups <= numOfCups; cups += 1) {
    const teaCup = prepareTea();
    teaCups.push(teaCup);
  }
  return teaCups;
};

// Only change code below this line
const tea4GreenTeamFCC = null;
const tea4BlackTeamFCC = null;
// Only change code above this line

console.log(
  tea4GreenTeamFCC,
  tea4BlackTeamFCC
);
```

# --solutions--

```js
const prepareGreenTea = () => 'greenTea';
const prepareBlackTea = () => 'blackTea';

const getTea = (prepareTea, numOfCups) => {
  const teaCups = [];

  for(let cups = 1; cups <= numOfCups; cups += 1) {
    const teaCup = prepareTea();
    teaCups.push(teaCup);
  }
  return teaCups;
};

const tea4BlackTeamFCC = getTea(prepareBlackTea, 13);
const tea4GreenTeamFCC = getTea(prepareGreenTea, 27);
```