---
id: 587d7dae367417b2b2512b7b
title: Understand Own Properties
challengeType: 1
forumTopicId: 301326
localeTitle: 了解自己的属性
---

## Description
<section id='description'>
请看下面的实例，<code>Bird</code>构造函数定义了两个属性：<code>name</code>和<code>numLegs</code>：

```js
function Bird(name) {
  this.name  = name;
  this.numLegs = 2;
}

let duck = new Bird("Donald");
let canary = new Bird("Tweety");
```

<code>name</code>和<code>numLegs</code>被叫做<code>自身</code>属性，因为他们是直接在实例对象上定义的。这就意味着<code>duck</code>和<code>canary</code>这两个对象分别拥有这些属性的独立副本。
事实上，<code>Bird</code>的这些实例都将拥有这些属性的独立副本。
以下的代码将<code>duck</code>里面所有的<code>自身</code>属性都存到一个叫<code>ownProps</code>的数组里面：

```js
let ownProps = [];

for (let property in duck) {
  if(duck.hasOwnProperty(property)) {
    ownProps.push(property);
  }
}

console.log(ownProps); // prints [ "name", "numLegs" ]
```

</section>

## Instructions
<section id='instructions'>
将<code>canary</code>对象里面的<code>自身</code>属性添加到<code>ownProps</code>数组里面。
</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: "<code>ownProps</code>应该包含<code>'numLegs'</code>和<code>'name'</code>两个属性的值。"
    testString: assert(ownProps.indexOf('name') !== -1 && ownProps.indexOf('numLegs') !== -1);
  - text: 在不使用内置方法<code>Object.keys()</code>的情况下完成这个挑战。
    testString: assert(!/Object(\.keys|\[(['"`])keys\2\])/.test(code));
  - text: You should solve this challenge without hardcoding the <code>ownProps</code> array.
    testString: assert(!/\[\s*(?:'|")(?:name|numLegs)|(?:push|concat)\(\s*(?:'|")(?:name|numLegs)/.test(code));

```

</section>

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

<div id='js-seed'>

```js
function Bird(name) {
  this.name = name;
  this.numLegs = 2;
}

let canary = new Bird("Tweety");
let ownProps = [];
// Add your code below this line



```

</div>



</section>

## Solution
<section id='solution'>


```js
function Bird(name) {
  this.name = name;
  this.numLegs = 2;
}

let canary = new Bird("Tweety");
function getOwnProps (obj) {
  const props = [];

  for (let prop in obj) {
    if (obj.hasOwnProperty(prop)) {
      props.push(prop);
    }
  }

  return props;
}

const ownProps = getOwnProps(canary);
```

</section>