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

id, title, challengeType, forumTopicId

id	title	challengeType	forumTopicId
587d7b8e367417b2b2512b5c	Understand Functional Programming Terminology	1	301240

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: Callbacks 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 first class 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 higher order functions. When the functions are passed in to another function or returned from another function, then those functions which gets passed in or returned can be called a lambda.

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.

Tests

tests:
  - text: The <code>tea4GreenTeamFCC</code> variable should hold 27 cups of green tea for the team.
    testString: assert(tea4GreenTeamFCC.length === 27);
  - text: The <code>tea4GreenTeamFCC</code> variable should hold cups of green tea.
    testString: assert(tea4GreenTeamFCC[0] === 'greenTea');
  - text: The <code>tea4BlackTeamFCC</code> variable should hold 13 cups of black tea.
    testString: assert(tea4BlackTeamFCC.length === 13);
  - text: The <code>tea4BlackTeamFCC</code> variable should hold cups of black tea.
    testString: assert(tea4BlackTeamFCC[0] === 'blackTea');

Challenge Seed

// 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
);

Solution

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);