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118 lines
4.4 KiB
Markdown
118 lines
4.4 KiB
Markdown
---
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id: 587d7b8e367417b2b2512b5c
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title: Understand Functional Programming Terminology
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challengeType: 1
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---
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## Description
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<section id='description'>
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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.
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With that information, we'll need to revisit the <code>getTea</code> function from last challenge to handle various tea requests. We can modify <code>getTea</code> to accept a function as a parameter to be able to change the type of tea it prepares. This makes <code>getTea</code> more flexible, and gives the programmer more control when client requests change.
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But first, let's cover some functional terminology:
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<code>Callbacks</code> 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 <code>filter</code>, the callback function tells JavaScript the criteria for how to filter an array.
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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 <code>first class</code> functions. In JavaScript, all functions are <code>first class</code> functions.
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The functions that take a function as an argument, or return a function as a return value are called <code>higher order</code> functions.
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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 <code>lambda</code>.
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</section>
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## Instructions
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<section id='instructions'>
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Prepare 27 cups of green tea and 13 cups of black tea and store them in <code>tea4GreenTeamFCC</code> and <code>tea4BlackTeamFCC</code> variables, respectively. Note that the <code>getTea</code> function has been modified so it now takes a function as the first argument.
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Note: The data (the number of cups of tea) is supplied as the last argument. We'll discuss this more in later lessons.
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: The <code>tea4GreenTeamFCC</code> variable should hold 27 cups of green tea for the team.
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testString: assert(tea4GreenTeamFCC.length === 27, 'The <code>tea4GreenTeamFCC</code> variable should hold 27 cups of green tea for the team.');
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- text: The <code>tea4GreenTeamFCC</code> variable should hold cups of green tea.
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testString: assert(tea4GreenTeamFCC[0] === 'greenTea', 'The <code>tea4GreenTeamFCC</code> variable should hold cups of green tea.');
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- text: The <code>tea4BlackTeamFCC</code> variable should hold 13 cups of black tea.
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testString: assert(tea4BlackTeamFCC.length === 13, 'The <code>tea4BlackTeamFCC</code> variable should hold 13 cups of black tea.');
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- text: The <code>tea4BlackTeamFCC</code> variable should hold cups of black tea.
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testString: assert(tea4BlackTeamFCC[0] === 'blackTea', 'The <code>tea4BlackTeamFCC</code> variable should hold cups of black tea.');
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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/**
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* A long process to prepare green tea.
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* @return {string} A cup of green tea.
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**/
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const prepareGreenTea = () => 'greenTea';
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/**
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* A long process to prepare black tea.
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* @return {string} A cup of black tea.
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**/
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const prepareBlackTea = () => 'blackTea';
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/**
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* Get given number of cups of tea.
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* @param {function():string} prepareTea The type of tea preparing function.
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* @param {number} numOfCups Number of required cups of tea.
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* @return {Array<string>} Given amount of tea cups.
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**/
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const getTea = (prepareTea, numOfCups) => {
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const teaCups = [];
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for(let cups = 1; cups <= numOfCups; cups += 1) {
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const teaCup = prepareTea();
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teaCups.push(teaCup);
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}
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return teaCups;
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};
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// Add your code below this line
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const tea4GreenTeamFCC = null; // :(
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const tea4BlackTeamFCC = null; // :(
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// Add your code above this line
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console.log(
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tea4GreenTeamFCC,
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tea4BlackTeamFCC
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);
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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// solution required
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const prepareGreenTea = () => 'greenTea';
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const prepareBlackTea = () => 'blackTea';
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const getTea = (prepareTea, numOfCups) => {
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const teaCups = [];
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for(let cups = 1; cups <= numOfCups; cups += 1) {
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const teaCup = prepareTea();
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teaCups.push(teaCup);
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}
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return teaCups;
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};
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const tea4BlackTeamFCC = getTea(prepareBlackTea, 13);
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const tea4GreenTeamFCC = getTea(prepareGreenTea, 27);
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```
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</section>
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