79 lines
3.2 KiB
Markdown
79 lines
3.2 KiB
Markdown
|
---
|
|||
|
|
id: 587d7b7d367417b2b2512b1c
|
|||
|
|
title: Check if an Object has a Property
|
|||
|
|
challengeType: 1
|
|||
|
|
videoUrl: ''
|
|||
|
|
localeTitle: 检查对象是否具有属性
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Description
|
|||
|
|
<section id="description">现在我们可以添加，修改和删除对象中的键。但是，如果我们只是想知道某个对象是否具有特定属性呢？ JavaScript为我们提供了两种不同的方法。一个使用<code>hasOwnProperty()</code>方法，另一个使用<code>in</code>关键字。如果我们有一个具有<code>Alan</code>属性的对象<code>users</code> ，我们可以通过以下任一方式检查其存在： <blockquote> users.hasOwnProperty（ '艾伦'）; <br> '艾伦'在用户; <br> //都返回true </blockquote></section>
|
|||
|
|
|
|||
|
|
## Instructions
|
|||
|
|
<section id="instructions">我们创建了一个对象， <code>users</code> ，其中包含一些用户和一个函数<code>isEveryoneHere</code> ，我们将<code>users</code>对象作为参数传递给它。完成编写此函数，以便仅当<code>users</code>对象包含所有四个名称（ <code>Alan</code> ， <code>Jeff</code> ， <code>Sarah</code>和<code>Ryan</code> ）作为键时才返回<code>true</code> ，否则返回<code>false</code> 。 </section>
|
|||
|
|
|
|||
|
|
## Tests
|
|||
|
|
<section id='tests'>
|
|||
|
|
|
|||
|
|
```yml
|
|||
|
|
tests:
|
|||
|
|
- text: <code>users</code>对象仅包含<code>Alan</code> ， <code>Jeff</code> ， <code>Sarah</code>和<code>Ryan</code>
|
|||
|
|
testString: 'assert("Alan" in users && "Jeff" in users && "Sarah" in users && "Ryan" in users && Object.keys(users).length === 4, "The <code>users</code> object only contains the keys <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code>");'
|
|||
|
|
- text: 如果<code>Alan</code> ， <code>Jeff</code> ， <code>Sarah</code>和<code>Ryan</code>是<code>users</code>对象的属性，则函数<code>isEveryoneHere</code>返回<code>true</code>
|
|||
|
|
testString: 'assert(isEveryoneHere(users) === true, "The function <code>isEveryoneHere</code> returns <code>true</code> if <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code> are properties on the <code>users</code> object");'
|
|||
|
|
- text: 如果<code>Alan</code> ， <code>Jeff</code> ， <code>Sarah</code>和<code>Ryan</code>不是<code>users</code>对象的属性，则函数<code>isEveryoneHere</code>返回<code>false</code>
|
|||
|
|
testString: 'assert((function() { delete users.Alan; delete users.Jeff; delete users.Sarah; delete users.Ryan; return isEveryoneHere(users) })() === false, "The function <code>isEveryoneHere</code> returns <code>false</code> if <code>Alan</code>, <code>Jeff</code>, <code>Sarah</code>, and <code>Ryan</code> are not properties on the <code>users</code> object");'
|
|||
|
|
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
## Challenge Seed
|
|||
|
|
<section id='challengeSeed'>
|
|||
|
|
|
|||
|
|
<div id='js-seed'>
|
|||
|
|
|
|||
|
|
```js
|
|||
|
|
let users = {
|
|||
|
|
Alan: {
|
|||
|
|
age: 27,
|
|||
|
|
online: true
|
|||
|
|
},
|
|||
|
|
Jeff: {
|
|||
|
|
age: 32,
|
|||
|
|
online: true
|
|||
|
|
},
|
|||
|
|
Sarah: {
|
|||
|
|
age: 48,
|
|||
|
|
online: true
|
|||
|
|
},
|
|||
|
|
Ryan: {
|
|||
|
|
age: 19,
|
|||
|
|
online: true
|
|||
|
|
}
|
|||
|
|
};
|
|||
|
|
|
|||
|
|
function isEveryoneHere(obj) {
|
|||
|
|
// change code below this line
|
|||
|
|
|
|||
|
|
// change code above this line
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
console.log(isEveryoneHere(users));
|
|||
|
|
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
## Solution
|
|||
|
|
<section id='solution'>
|
|||
|
|
|
|||
|
|
```js
|
|||
|
|
// solution required
|
|||
|
|
```
|
|||
|
|
</section>
|