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---
id: cf1111c1c12feddfaeb3bdef
title: 用 if 語句來表達條件邏輯
challengeType: 1
videoUrl: 'https://scrimba.com/c/cy87mf3'
forumTopicId: 18348
dashedName: use-conditional-logic-with-if-statements
---
# --description--
`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)。
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。
**僞代碼**
<blockquote>if<i>條件爲真</i>{<br> <i>語句被執行</i><br>}</blockquote>
**示例**
```js
function test (myCondition) {
if (myCondition) {
return "It was true";
}
return "It was false";
}
test(true);
test(false);
```
`test(true)` 返回字符串 `It was true``test(false)` 返回字符串 `It was false`
`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*`true`,並且不執行大括號後面的語句,函數返回 `It was false`
# --instructions--
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`
# --hints--
`trueOrFalse` 應該是一個函數
```js
assert(typeof trueOrFalse === 'function');
```
`trueOrFalse(true)` 應該返回一個字符串
```js
assert(typeof trueOrFalse(true) === 'string');
```
`trueOrFalse(false)` 應該返回一個字符串
```js
assert(typeof trueOrFalse(false) === 'string');
```
`trueOrFalse(true)` 應該返回 `Yes, that was true`
```js
assert(trueOrFalse(true) === 'Yes, that was true');
```
`trueOrFalse(false)`應該返回 `No, that was false`
```js
assert(trueOrFalse(false) === 'No, that was false');
```
# --seed--
## --seed-contents--
```js
function trueOrFalse(wasThatTrue) {
// Only change code below this line
// Only change code above this line
}
```
# --solutions--
```js
function trueOrFalse(wasThatTrue) {
if (wasThatTrue) {
return "Yes, that was true";
}
return "No, that was false";
}
```