.github
api-server
client
config
curriculum
challenges
_meta
arabic
chinese
01-responsive-web-design
02-javascript-algorithms-and-data-structures
basic-algorithm-scripting
basic-data-structures
-iterate-through-the-keys-of-an-object-with-a-for...in-statement.chinese.md
access-an-arrays-contents-using-bracket-notation.chinese.md
access-property-names-with-bracket-notation.chinese.md
add-items-to-an-array-with-push-and-unshift.chinese.md
add-items-using-splice.chinese.md
add-key-value-pairs-to-javascript-objects.chinese.md
check-for-the-presence-of-an-element-with-indexof.chinese.md
check-if-an-object-has-a-property.chinese.md
combine-arrays-with-the-spread-operator.chinese.md
copy-an-array-with-the-spread-operator.chinese.md
copy-array-items-using-slice.chinese.md
create-complex-multi-dimensional-arrays.chinese.md
generate-an-array-of-all-object-keys-with-object.keys.chinese.md
iterate-through-all-an-arrays-items-using-for-loops.chinese.md
modify-an-array-stored-in-an-object.chinese.md
modify-an-object-nested-within-an-object.chinese.md
remove-items-from-an-array-with-pop-and-shift.chinese.md
remove-items-using-splice.chinese.md
use-an-array-to-store-a-collection-of-data.chinese.md
use-the-delete-keyword-to-remove-object-properties.chinese.md
basic-javascript
debugging
es6
functional-programming
intermediate-algorithm-scripting
javascript-algorithms-and-data-structures-projects
object-oriented-programming
regular-expressions
03-front-end-libraries
04-data-visualization
06-information-security-and-quality-assurance
08-coding-interview-prep
09-certificates
english
portuguese
russian
spanish
formattingConversion
math-challenges
requiresTests
schema
test
.babelrc
.editorconfig
.npmignore
.travis.yml
CHANGELOG.md
LICENSE.md
commitizen.config.js
commitlint.config.js
create-challenge-bundle.js
getChallenges.js
gulpfile.js
index.js
lib.js
md-translation.js
package-entry.js
package-lock.json
package.json
utils.js
docs
guide
mock-guide
tools
.editorconfig
.eslintignore
.eslintrc.json
.gitattributes
.gitignore
.node-inspectorrc
.prettierrc
.snyk
.travis.yml
.vcmrc
CODE_OF_CONDUCT.md
CONTRIBUTING.md
Dockerfile.tests
LICENSE.md
README.french.md
README.italian.md
README.md
change_volumes_owner.sh
docker-compose-shared.yml
docker-compose.tests.yml
docker-compose.yml
lerna.json
netlify.toml
package-lock.json
package.json
sample.env
74 lines
3.3 KiB
Markdown
74 lines
3.3 KiB
Markdown
|
---
|
|||
|
|
id: 587d7b7c367417b2b2512b1a
|
|||
|
|
title: Access Property Names with Bracket Notation
|
|||
|
|
challengeType: 1
|
|||
|
|
videoUrl: ''
|
|||
|
|
localeTitle: 使用括号表示法访问属性名称
|
|||
|
|
---
|
|||
|
|
|
|||
|
|
## Description
|
|||
|
|
<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>
|
|||
|
|
|
|||
|
|
## Instructions
|
|||
|
|
<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>
|
|||
|
|
|
|||
|
|
## Tests
|
|||
|
|
<section id='tests'>
|
|||
|
|
|
|||
|
|
```yml
|
|||
|
|
tests:
|
|||
|
|
- text: <code>checkInventory</code>是一个函数
|
|||
|
|
testString: 'assert.strictEqual(typeof checkInventory, "function", "<code>checkInventory</code> is a function");'
|
|||
|
|
- 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>'
|
|||
|
|
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>");'
|
|||
|
|
- text: <code>checkInventory("apples")</code>应该返回<code>25</code>
|
|||
|
|
testString: 'assert.strictEqual(checkInventory("apples"), 25, "<code>checkInventory("apples")</code> should return <code>25</code>");'
|
|||
|
|
- text: <code>checkInventory("bananas")</code>应该返回<code>13</code>
|
|||
|
|
testString: 'assert.strictEqual(checkInventory("bananas"), 13, "<code>checkInventory("bananas")</code> should return <code>13</code>");'
|
|||
|
|
- text: <code>checkInventory("strawberries")</code>应该返回<code>27</code>
|
|||
|
|
testString: 'assert.strictEqual(checkInventory("strawberries"), 27, "<code>checkInventory("strawberries")</code> should return <code>27</code>");'
|
|||
|
|
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
## Challenge Seed
|
|||
|
|
<section id='challengeSeed'>
|
|||
|
|
|
|||
|
|
<div id='js-seed'>
|
|||
|
|
|
|||
|
|
```js
|
|||
|
|
let foods = {
|
|||
|
|
apples: 25,
|
|||
|
|
oranges: 32,
|
|||
|
|
plums: 28,
|
|||
|
|
bananas: 13,
|
|||
|
|
grapes: 35,
|
|||
|
|
strawberries: 27
|
|||
|
|
};
|
|||
|
|
// do not change code above this line
|
|||
|
|
|
|||
|
|
function checkInventory(scannedItem) {
|
|||
|
|
// change code below this line
|
|||
|
|
|
|||
|
|
}
|
|||
|
|
|
|||
|
|
// change code below this line to test different cases:
|
|||
|
|
console.log(checkInventory("apples"));
|
|||
|
|
|
|||
|
|
```
|
|||
|
|
|
|||
|
|
</div>
|
|||
|
|
|
|||
|
|
|
|||
|
|
|
|||
|
|
</section>
|
|||
|
|
|
|||
|
|
## Solution
|
|||
|
|
<section id='solution'>
|
|||
|
|
|
|||
|
|
```js
|
|||
|
|
// solution required
|
|||
|
|
```
|
|||
|
|
</section>
|