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 语句来表达条件逻辑
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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` 语句用于在代码中做出决定。 关键字 `if` 告诉 JavaScript 在小括号中的条件为真的情况下去执行定义在大括号里面的代码。 这种条件被称为 `Boolean` 条件，因为他们只可能是 `true`（真）或 `false`（假）。
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当条件的计算结果为 `true`，程序执行大括号内的语句。 当布尔条件的计算结果为 `false`，大括号内的代码将不会执行。
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**伪代码**
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<blockquote>if（<i>条件为真</i>）{<br> <i>语句被执行</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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当 `test` 被调用，并且传递进来的参数值为 `true` 时，`if` 语句会计算 `myCondition` 的结果，看它是否为 `true`。 如果条件为 `true`，函数会返回 `It was true`。 当 `test` 被调用，并且传递进来的参数值为 `false` 时，`myCondition` *不* 为 `true`，并且不执行大括号后面的语句，函数返回 `It was false`。
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# --instructions--
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在函数内部创建一个 `if` 语句，如果该参数 `wasThatTrue` 值为 `true`，返回 `Yes, that was true`，否则，返回`No, that was false`。
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# --hints--
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`trueOrFalse` 应该是一个函数
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```js
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assert(typeof trueOrFalse === 'function');
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```
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`trueOrFalse(true)` 应该返回一个字符串
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```js
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assert(typeof trueOrFalse(true) === 'string');
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```
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`trueOrFalse(false)` 应该返回一个字符串
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```js
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assert(typeof trueOrFalse(false) === 'string');
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```
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`trueOrFalse(true)` 应该返回 `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)`应该返回 `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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