72 lines
2.5 KiB
Markdown
72 lines
2.5 KiB
Markdown
---
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id: 598f48a36c8c40764b4e52b3
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title: Prevent Object Mutation
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challengeType: 1
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videoUrl: ''
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localeTitle: 防止对象突变
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---
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## Description
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<section id="description">正如之前的挑战所示， <code>const</code>声明本身并不能真正保护您的数据免受突变。为确保您的数据不会发生变化，JavaScript提供了一个<code>Object.freeze</code>函数来防止数据突变。对象冻结后，您将无法再从中添加，更新或删除属性。任何更改对象的尝试都将被拒绝而不会出现错误。 <blockquote>让obj = { <br>名称：“FreeCodeCamp” <br>点评：“真棒” <br> }; <br> Object.freeze（OBJ）; <br> obj.review =“坏”; //将被忽略。不允许变异<br> obj.newProp =“测试”; //将被忽略。不允许变异<br>的console.log（OBJ）; <br> // {name：“FreeCodeCamp”，评论：“很棒”} </blockquote></section>
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## Instructions
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<section id="instructions">在这个挑战中，您将使用<code>Object.freeze</code>来防止数学常量发生变化。您需要冻结<code>MATH_CONSTANTS</code>对象，以便没有人能够更改<code>PI</code>的值，添加或删除属性。 </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: 不要替换<code>const</code>关键字。
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testString: 'getUserInput => assert(getUserInput("index").match(/const/g), "Do not replace <code>const</code> keyword.");'
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- text: <code>MATH_CONSTANTS</code>应该是一个常量变量（使用<code>const</code> ）。
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testString: 'getUserInput => assert(getUserInput("index").match(/const\s+MATH_CONSTANTS/g), "<code>MATH_CONSTANTS</code> should be a constant variable (by using <code>const</code>).");'
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- text: 请勿更改原始<code>MATH_CONSTANTS</code> 。
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testString: 'getUserInput => assert(getUserInput("index").match(/const\s+MATH_CONSTANTS\s+=\s+{\s+PI:\s+3.14\s+};/g), "Do not change original <code>MATH_CONSTANTS</code>.");'
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- text: <code>PI</code>等于<code>3.14</code> 。
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testString: 'assert(PI === 3.14, "<code>PI</code> equals <code>3.14</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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function freezeObj() {
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"use strict";
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const MATH_CONSTANTS = {
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PI: 3.14
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};
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// change code below this line
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// change code above this line
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try {
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MATH_CONSTANTS.PI = 99;
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} catch( ex ) {
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console.log(ex);
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}
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return MATH_CONSTANTS.PI;
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}
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const PI = freezeObj();
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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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