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115 lines
2.3 KiB
Markdown
115 lines
2.3 KiB
Markdown
---
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id: 56533eb9ac21ba0edf2244dd
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title: 使用 Switch 语句从许多选项中进行选择
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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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dashedName: selecting-from-many-options-with-switch-statements
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---
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# --description--
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If you need to match one value against many options, you can use a <dfn>switch</dfn> statement. A `switch` statement compares the value to the <dfn>case</dfn> statements which define various possible values. Any valid JavaScript statements can be executed inside a <dfn>case</dfn> block and will run from the first matched `case` value until a `break` is encountered.
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这是 `switch` 语句的示例：
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```js
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switch (fruit) {
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case "apple":
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console.log("The fruit is an apple");
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break;
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case "orange":
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console.log("The fruit is an orange");
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break;
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}
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```
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测试 `case` 值使用严格相等（`===`）运算符进行比较。 `break` 告诉 JavaScript 停止执行 switch 语句。 如果遗漏了 `break` ，下一个语句将会被执行。
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# --instructions--
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写一个测试 `val` 的 switch 语句，并且根据下面的条件来设置不同的 `answer`：
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`1` - `alpha`
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`2` - `beta`
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`3` - `gamma`
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`4` - `delta`
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# --hints--
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`caseInSwitch(1)` 值应该为字符串 `alpha`
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```js
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assert(caseInSwitch(1) === 'alpha');
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```
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`caseInSwitch(2)` 值应该为字符串 `beta`
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```js
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assert(caseInSwitch(2) === 'beta');
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```
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`caseInSwitch(3)` 值应该为字符串 `gamma`
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```js
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assert(caseInSwitch(3) === 'gamma');
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```
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`caseInSwitch(4)` 值应该为字符串 `delta`
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```js
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assert(caseInSwitch(4) === 'delta');
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```
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不能使用任何 `if` 或 `else` 表达式
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```js
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assert(!/else/g.test(code) || !/if/g.test(code));
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```
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你应该有至少 3 个 `break` 表达式
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```js
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assert(code.match(/break/g).length > 2);
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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 caseInSwitch(val) {
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let 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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caseInSwitch(1);
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```
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# --solutions--
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```js
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function caseInSwitch(val) {
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let 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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