74 lines
3.3 KiB
Markdown
74 lines
3.3 KiB
Markdown
---
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id: 587d7b7c367417b2b2512b1a
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title: Access Property Names with Bracket Notation
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challengeType: 1
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videoUrl: ''
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localeTitle: 使用括号表示法访问属性名称
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---
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## Description
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<section id="description">在第一个对象挑战中，我们提到使用括号表示法作为使用变量求值来访问属性值的方法。例如，假设我们的<code>foods</code>对象被用于超市收银机的程序中。我们有一些设置<code>selectedFood</code>功能，我们想检查我们的<code>foods</code>对象是否存在该食物。这可能看起来像： <blockquote> let selectedFood = getCurrentFood（scanningItem）; <br>让库存=食物[selectedFood]; </blockquote>此代码将评估存储在<code>selectedFood</code>变量中的值，并在<code>foods</code>对象中返回该键的值，如果不存在则返回<code>undefined</code> 。括号表示法非常有用，因为有时候对象属性在运行时之前是未知的，或者我们需要以更动态的方式访问它们。 </section>
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## Instructions
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<section id="instructions">我们定义了一个函数<code>checkInventory</code> ，它接收一个扫描的项目作为参数。返回<code>foods</code>对象中的<code>scannedItem</code>键的当前值。您可以假设只有有效键将作为<code>checkInventory</code>的参数提供。 </section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: <code>checkInventory</code>是一个函数
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testString: 'assert.strictEqual(typeof checkInventory, "function", "<code>checkInventory</code> is a function");'
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- text: '<code>foods</code>对象应该只有以下键值对： <code>apples: 25</code> ， <code>oranges: 32</code> ， <code>plums: 28</code> ， <code>bananas: 13</code> ， <code>grapes: 35</code> ， <code>strawberries: 27</code>'
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testString: 'assert.deepEqual(foods, {apples: 25, oranges: 32, plums: 28, bananas: 13, grapes: 35, strawberries: 27}, "The <code>foods</code> object should have only the following key-value pairs: <code>apples: 25</code>, <code>oranges: 32</code>, <code>plums: 28</code>, <code>bananas: 13</code>, <code>grapes: 35</code>, <code>strawberries: 27</code>");'
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- text: <code>checkInventory("apples")</code>应该返回<code>25</code>
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testString: 'assert.strictEqual(checkInventory("apples"), 25, "<code>checkInventory("apples")</code> should return <code>25</code>");'
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- text: <code>checkInventory("bananas")</code>应该返回<code>13</code>
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testString: 'assert.strictEqual(checkInventory("bananas"), 13, "<code>checkInventory("bananas")</code> should return <code>13</code>");'
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- text: <code>checkInventory("strawberries")</code>应该返回<code>27</code>
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testString: 'assert.strictEqual(checkInventory("strawberries"), 27, "<code>checkInventory("strawberries")</code> should return <code>27</code>");'
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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let foods = {
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apples: 25,
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oranges: 32,
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plums: 28,
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bananas: 13,
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grapes: 35,
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strawberries: 27
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};
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// do not change code above this line
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function checkInventory(scannedItem) {
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// change code below this line
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}
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// change code below this line to test different cases:
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console.log(checkInventory("apples"));
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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// solution required
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```
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</section>
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