66 lines
2.9 KiB
Markdown
66 lines
2.9 KiB
Markdown
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---
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id: 587d7b86367417b2b2512b3b
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title: Catch Off By One Errors When Using Indexing
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challengeType: 1
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videoUrl: ''
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localeTitle: 使用索引时捕获一个错误
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---
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## Description
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<section id="description">当您尝试定位字符串或数组的特定索引（切片或访问段）或循环索引时，会<code>Off by one errors</code> （有时称为OBOE）。 JavaScript索引从零开始，而不是一个，这意味着最后一个索引总是小于项目的长度。如果您尝试访问等于长度的索引，程序可能会抛出“索引超出范围”引用错误或打印<code>undefined</code> 。当您使用将索引范围作为参数的字符串或数组方法时，它有助于阅读文档并了解它们是否包含（指定索引处的项目是否是返回的一部分）。以下是一些错误的示例： <blockquote> let alphabet =“abcdefghijklmnopqrstuvwxyz”; <br>让len = alphabet.length; <br> for（let i = 0; i <= len; i ++）{ <br> //最后循环一次太多次<br>的console.log（字母[I]）; <br> } <br> for（let j = 1; j <len; j ++）{ <br> //循环一次太少次并错过索引0处的第一个字符<br>的console.log（字母[J]）; <br> } <br> for（let k = 0; k <len; k ++）{ <br> // Goldilocks赞成 - 这是正确的<br>的console.log（字母表[K]）; <br> } </blockquote></section>
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## Instructions
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<section id="instructions">修复以下函数中的两个索引错误，以便将所有数字1到5打印到控制台。 </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: 您的代码应该设置循环的初始条件，以便从第一个索引开始。
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testString: 'assert(code.match(/i\s*?=\s*?0\s*?;/g).length == 1, "Your code should set the initial condition of the loop so it starts at the first index.");'
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- text: 您的代码应该修复循环的初始条件，以便索引从0开始。
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testString: 'assert(!code.match(/i\s?=\s*?1\s*?;/g), "Your code should fix the initial condition of the loop so that the index starts at 0.");'
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- text: 您的代码应设置循环的终端条件，以便它停在最后一个索引处。
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testString: 'assert(code.match(/i\s*?<\s*?len\s*?;/g).length == 1, "Your code should set the terminal condition of the loop so it stops at the last index.");'
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- text: 您的代码应该修复循环的终端条件，使其在长度之前停止在1。
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testString: 'assert(!code.match(/i\s*?<=\s*?len;/g), "Your code should fix the terminal condition of the loop so that it stops at 1 before the length.");'
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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 countToFive() {
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let firstFive = "12345";
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let len = firstFive.length;
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// Fix the line below
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for (let i = 1; i <= len; i++) {
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// Do not alter code below this line
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console.log(firstFive[i]);
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}
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}
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countToFive();
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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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