feat(curriculum): introduce let and const earlier (#43133)
* fix: move "Explore Differences Between..." to basic JS, update seed and tests * fix: resequence "Declare String Variables" * fix: move "Declare a Read-Only Variable..." to basic JS, update seed and tests * fix: revert changes to non-English "Explore Differences Between..." test text * fix: revert test strings, solutions, and seeds for non-English challenges * fix: update "Declare String Variables" description * fix: sync quotation marks in description and seed * fix: modify note in "Declare a Read-Only..." challenge * fix: update operator and compound assignment challenges * fix: update string challenges * fix: update array and array method challenges * fix: update function and scope challenges, resequence slightly * fix: "Word Blanks" solution * fix: add spacing to seed * fix: concatenating += challenge spacing * fix: appending variables to strings spacing * fix: find the length of a string spacing * fix: removed instances of removedFromMyArray = 0 * fix: switch challenges * fix: function argument and param spacing * fix: update counting cards, object challenges, and record collection * fix: finish rest of Basic JS section * fix: introducing else statements solution * fix: update spacing and wording * fix: update wording for const challenge * fix: update functional programming challenges * fix: intermediate algorithms and cert challenges * fix: revert some spacing and remove comments for fp challenge solutions * feat: add notes with links to moved let and const challenges in first two es6 challenges * fix: update es6 intro text * Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/concatenating-strings-with-the-plus-equals-operator.md Co-authored-by: Shaun Hamilton <shauhami020@gmail.com> * Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/finding-a-remainder-in-javascript.md Co-authored-by: Shaun Hamilton <shauhami020@gmail.com> * Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/global-scope-and-functions.md Co-authored-by: Shaun Hamilton <shauhami020@gmail.com> * Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/iterate-through-an-array-with-a-for-loop.md Co-authored-by: Shaun Hamilton <shauhami020@gmail.com> * Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/iterate-through-an-array-with-a-for-loop.md Co-authored-by: Shaun Hamilton <shauhami020@gmail.com> * Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/implement-map-on-a-prototype.md Co-authored-by: Shaun Hamilton <shauhami020@gmail.com> * Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/declare-a-read-only-variable-with-the-const-keyword.md Co-authored-by: Shaun Hamilton <shauhami020@gmail.com> * fix: concatenating strings with plus operator seed * fix: add comments back to Declare a Read-Only Variable... seed * feat: add es6 to basic javascript redirect tests for let and const challenges * fix: revert "Concatenating Strings with Plus Operator" seed * fix: move test file to cypress/integration/learn/redirects, separate redirect tests Co-authored-by: Shaun Hamilton <shauhami020@gmail.com>
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Kristofer Koishigawa
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@ -1,89 +0,0 @@
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---
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id: 587d7b87367417b2b2512b41
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title: 用 const 關鍵字聲明只讀變量
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challengeType: 1
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forumTopicId: 301201
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dashedName: declare-a-read-only-variable-with-the-const-keyword
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---
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# --description--
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`let` 並不是唯一的新的聲明變量的方式。 在 ES6 裏面，你還可以使用 `const` 關鍵字來聲明變量。
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`const` 擁有 `let` 的所有優點，不同的是，通過 `const` 聲明的變量是隻讀的。 這意味着通過 `const` 聲明的變量只能被賦值一次，而不能被再次賦值。
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```js
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const FAV_PET = "Cats";
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FAV_PET = "Dogs";
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```
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控制檯將由於給 `FAV_PET` 重新賦值而顯示錯誤。
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可見，嘗試給用 `const` 聲明的變量重新賦值會報錯。 你應該使用 `const` 關鍵字來聲明所有不打算再次賦值的變量。 這有助於避免給一個常量進行額外的再次賦值。 一個最佳實踐是對所有常量的命名採用全大寫字母，並在單詞之間使用下劃線進行分隔。
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**注意：**通常，開發者會用大寫字母作爲常量標識符，用小寫字母或者駝峯命名作爲變量（對象或數組）標識符。 後面的挑戰會涉及到在數組中使用小寫變量標識符。
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# --instructions--
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改變以下代碼，使得所有的變量都使用 `let` 或 `const` 關鍵詞來聲明。 當變量將會改變的時候使用 `let` 關鍵字，當變量要保持常量的時候使用 `const` 關鍵字。 同時，對使用 `const` 聲明的變量按照最佳實踐重命名，變量名中的字母應該都是大寫的。
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# --hints--
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代碼中不應有 `var`。
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```js
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(getUserInput) => assert(!getUserInput('index').match(/var/g));
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```
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`SENTENCE` 應該是使用 `const` 聲明的常量。
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```js
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(getUserInput) => assert(getUserInput('index').match(/(const SENTENCE)/g));
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```
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`i` 應該是使用 `let`聲明的。
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```js
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(getUserInput) => assert(getUserInput('index').match(/(let i)/g));
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```
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`console.log` 應該修改爲用於打印 `SENTENCE` 變量。
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```js
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(getUserInput) =>
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assert(getUserInput('index').match(/console\.log\(\s*SENTENCE\s*\)\s*;?/g));
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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 printManyTimes(str) {
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// Only change code below this line
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var sentence = str + " is cool!";
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for (var i = 0; i < str.length; i+=2) {
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console.log(sentence);
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}
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// Only change code above this line
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}
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printManyTimes("freeCodeCamp");
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```
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# --solutions--
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```js
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function printManyTimes(str) {
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const SENTENCE = str + " is cool!";
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for (let i = 0; i < str.length; i+=2) {
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console.log(SENTENCE);
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}
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}
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printManyTimes("freeCodeCamp");
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```
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@ -1,91 +0,0 @@
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---
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id: 587d7b87367417b2b2512b3f
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title: 探索 var 和 let 關鍵字之間的差異
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challengeType: 1
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forumTopicId: 301202
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dashedName: explore-differences-between-the-var-and-let-keywords
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---
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# --description--
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使用 `var` 關鍵字來聲明變量，會出現重複聲明導致變量被覆蓋卻不會報錯的問題。
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```js
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var camper = 'James';
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var camper = 'David';
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console.log(camper);
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```
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這裏控制檯將顯示字符串 `David`。
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在上面的代碼中，`camper` 變量的初始值爲 `James`，然後又被覆蓋成了 `David`。 在小型的應用中，你可能不會遇到這樣的問題。但是當你的代碼規模變得更加龐大的時候，就可能會在不經意間覆蓋了之前定義的變量。 因爲這樣的情況不會報錯，所以搜索和修復 bug 會變得非常困難。
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在 ES6 中引入了新的關鍵字 `let` 來解決 `var` 關鍵字帶來的潛在問題。 如果你在上面的代碼中使用 `let` 關鍵字來代替 `var` 關鍵字，結果會是一個報錯。
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```js
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let camper = 'James';
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let camper = 'David';
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```
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你可以在瀏覽器的控制檯裏看見這個錯誤。 與 `var` 不同的是，當使用 `let` 的時候，同一名字的變量只能被聲明一次。 請注意 `"use strict"`。 這代表着開啓了嚴格模式，用於檢測常見的代碼錯誤以及“不安全”的行爲， 例如：
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```js
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"use strict";
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x = 3.14;
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```
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這將顯示一個錯誤 `x is not defined`。
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# --instructions--
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請更新這段代碼，只使用 `let` 關鍵字。
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# --hints--
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代碼中不應有 `var`
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```js
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(getUserInput) => assert(!getUserInput('index').match(/var/g));
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```
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`catName` 變量的值應該爲 `Oliver`
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```js
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assert(catName === 'Oliver');
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```
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`quote` 變量的值應該爲 `Oliver says Meow!`
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```js
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assert(quote === 'Oliver says Meow!');
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```
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# --seed--
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## --seed-contents--
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```js
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var catName;
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var quote;
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function catTalk() {
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"use strict";
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catName = "Oliver";
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quote = catName + " says Meow!";
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}
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catTalk();
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```
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# --solutions--
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```js
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let catName;
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let quote;
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function catTalk() {
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'use strict';
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catName = 'Oliver';
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quote = catName + ' says Meow!';
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}
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catTalk();
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```
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