109 lines
2.5 KiB
Markdown
109 lines
2.5 KiB
Markdown
---
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id: 56533eb9ac21ba0edf2244dd
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title: Selecting from Many Options with Switch Statements
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challengeType: 1
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videoUrl: 'https://scrimba.com/c/c4mv4fm'
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forumTopicId: 18277
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localeTitle: 使用 Switch 语句从许多选项中进行选择
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---
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## Description
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<section id='description'>
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如果你有非常多的选项需要选择，可以使用 switch 语句。根据不同的参数值会匹配上不同的 case 分支，语句会从第一个匹配的 case 分支开始执行，直到碰到 break 就结束。
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这是一个伪代码案例：
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```js
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switch(lowercaseLetter) {
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case "a":
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console.log("A");
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break;
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case "b":
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console.log("B");
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break;
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}
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```
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测试<code>case</code>值使用严格相等运算符进行比较，break 关键字告诉 JavaScript 停止执行语句。如果没有 break 关键字，下一个语句会继续执行。
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</section>
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## Instructions
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<section id='instructions'>
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写一个测试<code>val</code>的 switch 语句，并且根据下面的条件来设置不同的<code>answer</code>：<br><code>1</code>- "alpha"<br><code>2</code> - "beta"<br><code>3</code>- "gamma"<br><code>4</code> - "delta"
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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>caseInSwitch(1)</code> 应该有一个值为 "alpha"。
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testString: assert(caseInSwitch(1) === "alpha");
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- text: <code>caseInSwitch(2)</code> 应该有一个值为 "beta"。
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testString: assert(caseInSwitch(2) === "beta");
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- text: <code>caseInSwitch(3)</code> 应该有一个值为 "gamma"。
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testString: assert(caseInSwitch(3) === "gamma");
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- text: <code>caseInSwitch(4)</code> 应该有一个值为 "delta"。
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testString: assert(caseInSwitch(4) === "delta");
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- text: 不能使用任何<code>if</code>或<code>else</code>表达式。
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testString: assert(!/else/g.test(code) || !/if/g.test(code));
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- text: 你应该有至少 3 个<code>break</code>表达式。
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testString: assert(code.match(/break/g).length > 2);
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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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function caseInSwitch(val) {
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var answer = "";
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// Only change code below this line
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// Only change code above this line
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return answer;
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}
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// Change this value to test
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caseInSwitch(1);
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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 caseInSwitch(val) {
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var answer = "";
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switch(val) {
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case 1:
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answer = "alpha";
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break;
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case 2:
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answer = "beta";
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break;
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case 3:
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answer = "gamma";
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break;
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case 4:
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answer = "delta";
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}
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return answer;
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}
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```
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</section>
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