2018-10-10 22:03:03 +00:00
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---
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id: 587d7b88367417b2b2512b46
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2021-03-15 03:20:39 +00:00
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title: 设置函数的默认参数
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2018-10-10 22:03:03 +00:00
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challengeType: 1
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2020-08-04 07:13:35 +00:00
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forumTopicId: 301209
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2021-01-13 02:31:00 +00:00
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dashedName: set-default-parameters-for-your-functions
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2018-10-10 22:03:03 +00:00
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---
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2020-12-16 07:37:30 +00:00
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# --description--
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2021-03-15 03:20:39 +00:00
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ES6 里允许给函数传入<dfn>默认参数</dfn>,来构建更加灵活的函数。
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2020-12-16 07:37:30 +00:00
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2021-03-15 03:20:39 +00:00
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请看以下代码:
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2020-08-04 07:13:35 +00:00
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```js
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const greeting = (name = "Anonymous") => "Hello " + name;
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2021-03-15 03:20:39 +00:00
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console.log(greeting("John"));
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console.log(greeting());
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2020-08-04 07:13:35 +00:00
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```
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2021-03-15 03:20:39 +00:00
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控制台将显示字符串 `Hello John` 和 `Hello Anonymous`。
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默认参数会在参数没有被指定(值为 undefined)的时候起作用。 在上面的例子中,参数 `name` 会在没有得到新的值的时候,默认使用值 `Anonymous`。 你还可以给多个参数赋予默认值。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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# --instructions--
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2018-10-10 22:03:03 +00:00
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2021-06-30 15:17:19 +00:00
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给函数 `increment` 传入默认参数,使得在 `value` 没有被赋值的时候,默认给 `number` 加上 1。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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# --hints--
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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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`increment(5, 2)` 的结果应该是 `7`。
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2018-10-10 22:03:03 +00:00
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```js
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2020-12-16 07:37:30 +00:00
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assert(increment(5, 2) === 7);
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2018-10-10 22:03:03 +00:00
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```
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2021-03-15 03:20:39 +00:00
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`increment(5)` 的结果应该是 `6`。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert(increment(5) === 6);
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```
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2018-10-10 22:03:03 +00:00
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2021-03-15 03:20:39 +00:00
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参数 `value` 的默认值是 `1`。
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2018-10-10 22:03:03 +00:00
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```js
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2020-12-16 07:37:30 +00:00
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assert(code.match(/value\s*=\s*1/g));
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2018-10-10 22:03:03 +00:00
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```
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2020-08-04 07:13:35 +00:00
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2021-01-13 02:31:00 +00:00
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# --seed--
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## --seed-contents--
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```js
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// Only change code below this line
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const increment = (number, value) => number + value;
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// Only change code above this line
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```
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2020-12-16 07:37:30 +00:00
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# --solutions--
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2021-01-13 02:31:00 +00:00
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```js
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const increment = (number, value = 1) => number + value;
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```
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