freeCodeCamp/curriculum/challenges/chinese/02-javascript-algorithms-and-data-structures/basic-javascript/write-reusable-javascript-with-functions.md

---
id: 56bbb991ad1ed5201cd392cf
challengeType: 1
videoUrl: 'https://scrimba.com/c/cL6dqfy'
forumTopicId: 18378
localeTitle: 用函数编写可重用代码
---

## Description
<section id='description'>
在 JavaScript 中，我们可以把代码的重复部分抽取出来，放到一个<dfn>函数</dfn>中。
举个例子：

```js
function functionName() {
  console.log("Hello World");
}
```

你可以通过函数名<code>functionName</code>加上后面的小括号来调用这个函数，就像这样：
<code>functionName();</code>
每次调用函数时，它都会在控制台上打印消息<code>"Hello World"</code>。每次调用函数时，大括号之间的所有代码都将被执行。
</section>

## Instructions
<section id='instructions'>
<ol><li>先创建一个名为<code>reusableFunction</code>的函数，这个函数可以打印<code>"Hi World"</code>到控制台上。</li><li>然后调用这个函数。</li></ol>
</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>reusableFunction</code>应该是一个函数。
    testString: assert(typeof reusableFunction === 'function');
  - text: <code>reusableFunction</code>应该在控制台中输出 "Hi World"。
    testString: assert(hiWorldWasLogged);
  - text: 在你定义<code>reusableFunction</code>之后记得调用它。
    testString: assert(/^\s*reusableFunction\(\)\s*/m.test(code));

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js
// Example
function ourReusableFunction() {
  console.log("Heyya, World");
}

ourReusableFunction();

// Only change code below this line

```

</div>

### Before Test
<div id='js-setup'>

```js
var logOutput = "";
var originalConsole = console;
var nativeLog = console.log;
var hiWorldWasLogged = false;
function capture() {
    console.log = function (message) {
        if(message === 'Hi World')  hiWorldWasLogged = true;
        if(message && message.trim) logOutput = message.trim();
        if(nativeLog.apply) {
          nativeLog.apply(originalConsole, arguments);
        } else {
          var nativeMsg = Array.prototype.slice.apply(arguments).join(' ');
          nativeLog(nativeMsg);
        }
    };
}

function uncapture() {
  console.log = nativeLog;
}

capture();
```

</div>

### After Test
<div id='js-teardown'>

```js
uncapture();

if (typeof reusableFunction !== "function") { 
  (function() { return "reusableFunction is not defined"; })();
} else {
  (function() { return logOutput || "console.log never called"; })();
}
```

</div>

</section>

## Solution
<section id='solution'>


```js
function reusableFunction() {
  console.log("Hi World");
}
reusableFunction();
```

</section>