158 lines
2.6 KiB
Markdown
158 lines
2.6 KiB
Markdown
---
|
|
id: 56533eb9ac21ba0edf2244e0
|
|
title: 用一个 Switch 语句来替代多个 if else 语句
|
|
challengeType: 1
|
|
videoUrl: 'https://scrimba.com/c/c3JE8fy'
|
|
forumTopicId: 18266
|
|
dashedName: replacing-if-else-chains-with-switch
|
|
---
|
|
|
|
# --description--
|
|
|
|
如果你有多个选项需要选择，`switch` 语句写起来会比多个串联的 `if`/`else if` 语句容易些。 譬如:
|
|
|
|
```js
|
|
if (val === 1) {
|
|
answer = "a";
|
|
} else if (val === 2) {
|
|
answer = "b";
|
|
} else {
|
|
answer = "c";
|
|
}
|
|
```
|
|
|
|
可以被下面替代：
|
|
|
|
```js
|
|
switch(val) {
|
|
case 1:
|
|
answer = "a";
|
|
break;
|
|
case 2:
|
|
answer = "b";
|
|
break;
|
|
default:
|
|
answer = "c";
|
|
}
|
|
```
|
|
|
|
# --instructions--
|
|
|
|
把串联的 `if`/`else if` 语句改成 `switch` 语句。
|
|
|
|
# --hints--
|
|
|
|
不要使用 `else` 表达式。
|
|
|
|
```js
|
|
assert(!/else/g.test(code));
|
|
```
|
|
|
|
不要使用 `if` 表达式。
|
|
|
|
```js
|
|
assert(!/if/g.test(code));
|
|
```
|
|
|
|
你应该有至少 4 个 `break` 表达式。
|
|
|
|
```js
|
|
assert(code.match(/break/g).length >= 4);
|
|
```
|
|
|
|
`chainToSwitch("bob")` 应该是字符串 `Marley`
|
|
|
|
```js
|
|
assert(chainToSwitch('bob') === 'Marley');
|
|
```
|
|
|
|
`chainToSwitch(42)` 应该是字符串 `The Answer`
|
|
|
|
```js
|
|
assert(chainToSwitch(42) === 'The Answer');
|
|
```
|
|
|
|
`chainToSwitch(1)` 应该是字符串 `There is no #1`
|
|
|
|
```js
|
|
assert(chainToSwitch(1) === 'There is no #1');
|
|
```
|
|
|
|
`chainToSwitch(99)`应该为 `Missed me by this much!`。
|
|
|
|
```js
|
|
assert(chainToSwitch(99) === 'Missed me by this much!');
|
|
```
|
|
|
|
`chainToSwitch(7)` 应该是字符串 `Ate Nine`
|
|
|
|
```js
|
|
assert(chainToSwitch(7) === 'Ate Nine');
|
|
```
|
|
|
|
`chainToSwitch("John")` 应该为 `""` (empty string)。
|
|
|
|
```js
|
|
assert(chainToSwitch('John') === '');
|
|
```
|
|
|
|
`chainToSwitch(156)` 应该为 `""` (empty string)。
|
|
|
|
```js
|
|
assert(chainToSwitch(156) === '');
|
|
```
|
|
|
|
# --seed--
|
|
|
|
## --seed-contents--
|
|
|
|
```js
|
|
function chainToSwitch(val) {
|
|
let answer = "";
|
|
// Only change code below this line
|
|
|
|
if (val === "bob") {
|
|
answer = "Marley";
|
|
} else if (val === 42) {
|
|
answer = "The Answer";
|
|
} else if (val === 1) {
|
|
answer = "There is no #1";
|
|
} else if (val === 99) {
|
|
answer = "Missed me by this much!";
|
|
} else if (val === 7) {
|
|
answer = "Ate Nine";
|
|
}
|
|
|
|
// Only change code above this line
|
|
return answer;
|
|
}
|
|
|
|
chainToSwitch(7);
|
|
```
|
|
|
|
# --solutions--
|
|
|
|
```js
|
|
function chainToSwitch(val) {
|
|
let answer = "";
|
|
|
|
switch(val) {
|
|
case "bob":
|
|
answer = "Marley";
|
|
break;
|
|
case 42:
|
|
answer = "The Answer";
|
|
break;
|
|
case 1:
|
|
answer = "There is no #1";
|
|
break;
|
|
case 99:
|
|
answer = "Missed me by this much!";
|
|
break;
|
|
case 7:
|
|
answer = "Ate Nine";
|
|
}
|
|
return answer;
|
|
}
|
|
```
|