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

---
id: 587d7b8d367417b2b2512b5b
title: Learn About Functional Programming
challengeType: 1
forumTopicId: 301233
---

# --description--

Functional programming is a style of programming where solutions are simple, isolated functions, without any side effects outside of the function scope.

`INPUT -> PROCESS -> OUTPUT`

Functional programming is about:

1) Isolated functions - there is no dependence on the state of the program, which includes global variables that are subject to change

2) Pure functions - the same input always gives the same output

3) Functions with limited side effects - any changes, or mutations, to the state of the program outside the function are carefully controlled

# --instructions--

The members of freeCodeCamp happen to love tea.

In the code editor, the `prepareTea` and `getTea` functions are already defined for you. Call the `getTea` function to get 40 cups of tea for the team, and store them in the `tea4TeamFCC` variable.

# --hints--

The `tea4TeamFCC` variable should hold 40 cups of tea for the team.

```js
assert(tea4TeamFCC.length === 40);
```

The `tea4TeamFCC` variable should hold cups of green tea.

```js
assert(tea4TeamFCC[0] === 'greenTea');
```

# --seed--

## --seed-contents--

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

/*
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 = (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 tea4TeamFCC = null;
// Only change code above this line
```

# --solutions--

```js
const prepareTea = () => 'greenTea';

const getTea = (numOfCups) => {
  const teaCups = [];
  
  for(let cups = 1; cups <= numOfCups; cups += 1) {
    const teaCup = prepareTea();
    teaCups.push(teaCup);
  }

  return teaCups;
};

const tea4TeamFCC = getTea(40); 
```