105 lines
3.1 KiB
Markdown
105 lines
3.1 KiB
Markdown
---
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id: cf1111c1c12feddfaeb3bdef
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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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title: 用 if 语句来表达条件逻辑
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---
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## Description
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<section id='description'>
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<code>If</code>语句用于在代码中做条件判断。关键字<code>if</code>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<code>Boolean</code>条件，因为他们只可能是<code>true</code>（真）或<code>false</code>（假）。
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当条件的计算结果为<code>true</code>，程序执行大括号内的语句。当布尔条件的计算结果为<code>false</code>，大括号内的代码将不会执行。
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<strong>伪代码</strong>
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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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<strong>示例</strong>
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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); // returns "It was true"
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test(false); // returns "It was false"
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```
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当<code>test</code>被调用，并且传递进来的参数值为<code>true</code>，<code>if</code>语句会计算<code>myCondition</code>的结果，看它是真还是假。如果条件为<code>true</code>，函数会返回<code>"It was true"</code>。当<code>test</code>被调用，并且传递进来的参数值为<code>false</code>，<code>myCondition</code><em>不</em> 为<code>true</code>，并且不执行大括号后面的语句，函数返回<code>"It was false"</code>。
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</section>
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## Instructions
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<section id='instructions'>
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在函数内部创建一个<code>if</code>语句，如果该参数<code>wasThatTrue</code>值为<code>true</code>，返回<code>"Yes, that was true"</code>，否则，并返回<code>"No, that was false"</code>。
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>trueOrFalse</code>应该是一个函数。
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testString: assert(typeof trueOrFalse === "function");
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- text: <code>trueOrFalse(true)</code>应该返回一个字符串。
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testString: assert(typeof trueOrFalse(true) === "string");
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- text: <code>trueOrFalse(false)</code>应该返回一个字符串。
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testString: assert(typeof trueOrFalse(false) === "string");
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- text: <code>trueOrFalse(true)</code>应该返回 "Yes, that was true"。
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testString: assert(trueOrFalse(true) === "Yes, that was true");
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- text: <code>trueOrFalse(false)</code>应该返回 "No, that was false"。
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testString: assert(trueOrFalse(false) === "No, that was false");
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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// Example
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function ourTrueOrFalse(isItTrue) {
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if (isItTrue) {
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return "Yes, it's true";
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}
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return "No, it's false";
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}
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// Setup
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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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// Change this value to test
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trueOrFalse(true);
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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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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</section>
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