2021-05-05 10:13:49 -07:00
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---
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id: 587d7b8e367417b2b2512b5c
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title: 瞭解函數式編程術語
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challengeType: 1
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forumTopicId: 301240
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dashedName: understand-functional-programming-terminology
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---
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# --description--
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FCC 團隊需求有變更,現在想要兩種茶:綠茶(green tea)和紅茶(black tea)。 事實證明,用戶需求變更是很常見的。
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基於以上信息,我們需要重構上一節挑戰中的 `getTea` 函數來處理多種茶的請求。 我們可以修改 `getTea` 接受一個函數作爲參數,使它能夠修改茶的類型。 這讓 `getTea` 更靈活,也使需求變更時爲程序員提供更多控制權。
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首先,我們將介紹一些術語:
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<dfn>Callbacks</dfn> 是被傳遞到另一個函數中調用的函數。 你應該已經在其他函數中看過這個寫法,例如在 `filter` 中,回調函數告訴 JavaScript 以什麼規則過濾數組。
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函數就像其他正常值一樣,可以賦值給變量、傳遞給另一個函數,或從其它函數返回,這種函數叫做頭等 <dfn>first class</dfn> 函數。 在 JavaScript 中,所有函數都是頭等函數。
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將函數爲參數或返回值的函數叫做高階 ( <dfn>higher order</dfn>) 函數。
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2021-05-24 00:42:08 -07:00
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當函數被傳遞給另一個函數或從另一個函數返回時,那些傳入或返回的函數可以叫做 <dfn>lambda</dfn>。
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2021-05-05 10:13:49 -07:00
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# --instructions--
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準備 27 杯綠茶和 13 杯紅茶,分別存入 `tea4GreenTeamFCC` 和 `tea4BlackTeamFCC` 變量。 請注意,`getTea` 函數已經變了,現在它接收一個函數作爲第一個參數。
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注意:數據(茶的數量)作爲最後一個參數。 我們將在後面的課程中對此進行更多討論。
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# --hints--
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`tea4GreenTeamFCC` 變量應存有爲團隊準備的 27 杯茶。
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```js
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assert(tea4GreenTeamFCC.length === 27);
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```
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`tea4GreenTeamFCC` 變量應存有綠茶。
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```js
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assert(tea4GreenTeamFCC[0] === 'greenTea');
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```
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`tea4BlackTeamFCC` 變量應存有 13 杯紅茶。
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```js
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assert(tea4BlackTeamFCC.length === 13);
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```
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`tea4BlackTeamFCC` 變量應存有紅茶。
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```js
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assert(tea4BlackTeamFCC[0] === 'blackTea');
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```
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# --seed--
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## --seed-contents--
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```js
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// Function that returns a string representing a cup of green tea
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const prepareGreenTea = () => 'greenTea';
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// Function that returns a string representing a cup of black tea
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const prepareBlackTea = () => 'blackTea';
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/*
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Given a function (representing the tea type) and number of cups needed, the
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following function returns an array of strings (each representing a cup of
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a specific type of tea).
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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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// Only change code below this line
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const tea4GreenTeamFCC = null;
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const tea4BlackTeamFCC = null;
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// Only change 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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# --solutions--
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```js
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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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