99 lines
2.4 KiB
Markdown
99 lines
2.4 KiB
Markdown
---
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id: cf1111c1c12feddfaeb3bdef
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title: 用 if 語句來表達條件邏輯
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challengeType: 1
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videoUrl: 'https://scrimba.com/c/cy87mf3'
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forumTopicId: 18348
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dashedName: use-conditional-logic-with-if-statements
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---
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# --description--
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`if` 語句用於在代碼中做出決定。 關鍵字 `if` 告訴 JavaScript 在小括號中的條件爲真的情況下去執行定義在大括號裏面的代碼。 這種條件被稱爲 `Boolean` 條件，因爲他們只可能是 `true`（真）或 `false`（假）。
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當條件的計算結果爲 `true`，程序執行大括號內的語句。 當布爾條件的計算結果爲 `false`，大括號內的代碼將不會執行。
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**僞代碼**
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<blockquote>if（<i>條件爲真</i>）{<br> <i>語句被執行</i><br>}</blockquote>
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**示例**
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```js
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function test (myCondition) {
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if (myCondition) {
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return "It was true";
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}
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return "It was false";
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}
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test(true);
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test(false);
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```
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`test(true)` 返回字符串 `It was true`，`test(false)` 返回字符串 `It was false`。
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當 `test` 被調用，並且傳遞進來的參數值爲 `true` 時，`if` 語句會計算 `myCondition` 的結果，看它是否爲 `true`。 如果條件爲 `true`，函數會返回 `It was true`。 當 `test` 被調用，並且傳遞進來的參數值爲 `false` 時，`myCondition` *不* 爲 `true`，並且不執行大括號後面的語句，函數返回 `It was false`。
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# --instructions--
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在函數內部創建一個 `if` 語句，如果該參數 `wasThatTrue` 值爲 `true`，返回 `Yes, that was true`，否則，返回`No, that was false`。
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# --hints--
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`trueOrFalse` 應該是一個函數
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```js
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assert(typeof trueOrFalse === 'function');
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```
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`trueOrFalse(true)` 應該返回一個字符串
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```js
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assert(typeof trueOrFalse(true) === 'string');
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```
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`trueOrFalse(false)` 應該返回一個字符串
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```js
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assert(typeof trueOrFalse(false) === 'string');
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```
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`trueOrFalse(true)` 應該返回 `Yes, that was true`
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```js
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assert(trueOrFalse(true) === 'Yes, that was true');
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```
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`trueOrFalse(false)`應該返回 `No, that was false`
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```js
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assert(trueOrFalse(false) === 'No, that was false');
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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 trueOrFalse(wasThatTrue) {
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// Only change code below this line
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// Only change code above this line
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}
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```
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# --solutions--
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```js
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function trueOrFalse(wasThatTrue) {
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if (wasThatTrue) {
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return "Yes, that was true";
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}
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return "No, that was false";
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}
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```
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