66 lines
3.6 KiB
Markdown
66 lines
3.6 KiB
Markdown
|
---
|
|||
|
id: 587d7dba367417b2b2512ba9
|
|||
|
title: Positive and Negative Lookahead
|
|||
|
challengeType: 1
|
|||
|
videoUrl: ''
|
|||
|
localeTitle: 积极和消极的前瞻
|
|||
|
---
|
|||
|
|
|||
|
## Description
|
|||
|
<section id="description"> <code>Lookaheads</code>是一种模式,它告诉JavaScript在字符串中向前看以进一步检查模式。当您想要在同一个字符串上搜索多个模式时,这非常有用。有两种<code>lookaheads</code> : <code>positive lookahead</code>和<code>negative lookahead</code> 。一个<code>positive lookahead</code>向前看将确保搜索模式中的元素存在,但实际上不匹配它。正向前瞻用作<code>(?=...)</code> ,其中<code>...</code>是不匹配的必需部分。另一方面, <code>negative lookahead</code>将确保搜索模式中的元素不存在。负向前瞻用作<code>(?!...)</code> ,其中<code>...</code>是您不希望在那里的模式。如果不存在负前瞻部分,则返回模式的其余部分。前瞻有点令人困惑,但一些例子会有所帮助。 <blockquote>让quit =“qu”; <br>让noquit =“qt”; <br>让quRegex = / q(?= u)/; <br>让qRegex = / q(?!u)/; <br> quit.match(quRegex); //返回[“q”] <br> noquit.match(qRegex); //返回[“q”] </blockquote> <code>lookaheads</code>更实际用途是检查一个字符串中的两个或更多个模式。这是一个(天真)简单的密码检查器,可以查找3到6个字符和至少一个数字: <blockquote> let password =“abc123”; <br>让checkPass = /(?= \ w {3,6})(?= \ D * \ d)/; <br> checkPass.test(密码); //返回true </blockquote></section>
|
|||
|
|
|||
|
## Instructions
|
|||
|
<section id="instructions">使用<code>lookaheads</code>在<code>pwRegex</code>匹配长的时间大于5个字符,并有两个连续的数字密码。 </section>
|
|||
|
|
|||
|
## Tests
|
|||
|
<section id='tests'>
|
|||
|
|
|||
|
```yml
|
|||
|
tests:
|
|||
|
- text: 你的正则表达式应该使用两个积极的<code>lookaheads</code> 。
|
|||
|
testString: 'assert(pwRegex.source.match(/\(\?=.*?\)\(\?=.*?\)/) !== null, "Your regex should use two positive <code>lookaheads</code>.");'
|
|||
|
- text: 你的正则表达式不应该匹配<code>"astronaut"</code>
|
|||
|
testString: 'assert(!pwRegex.test("astronaut"), "Your regex should not match <code>"astronaut"</code>");'
|
|||
|
- text: 你的正则表达式不应该与<code>"airplanes"</code>匹配
|
|||
|
testString: 'assert(!pwRegex.test("airplanes"), "Your regex should not match <code>"airplanes"</code>");'
|
|||
|
- text: 你的正则表达式不应该匹配<code>"banan1"</code>
|
|||
|
testString: 'assert(!pwRegex.test("banan1"), "Your regex should not match <code>"banan1"</code>");'
|
|||
|
- text: 你的正则表达式应该匹配<code>"bana12"</code>
|
|||
|
testString: 'assert(pwRegex.test("bana12"), "Your regex should match <code>"bana12"</code>");'
|
|||
|
- text: 你的正则表达式应该匹配<code>"abc123"</code>
|
|||
|
testString: 'assert(pwRegex.test("abc123"), "Your regex should match <code>"abc123"</code>");'
|
|||
|
- text: 你的正则表达式不应该匹配<code>"123"</code>
|
|||
|
testString: 'assert(!pwRegex.test("123"), "Your regex should not match <code>"123"</code>");'
|
|||
|
- text: 你的正则表达式不应该匹配<code>"1234"</code>
|
|||
|
testString: 'assert(!pwRegex.test("1234"), "Your regex should not match <code>"1234"</code>");'
|
|||
|
|
|||
|
```
|
|||
|
|
|||
|
</section>
|
|||
|
|
|||
|
## Challenge Seed
|
|||
|
<section id='challengeSeed'>
|
|||
|
|
|||
|
<div id='js-seed'>
|
|||
|
|
|||
|
```js
|
|||
|
let sampleWord = "astronaut";
|
|||
|
let pwRegex = /change/; // Change this line
|
|||
|
let result = pwRegex.test(sampleWord);
|
|||
|
|
|||
|
```
|
|||
|
|
|||
|
</div>
|
|||
|
|
|||
|
|
|||
|
|
|||
|
</section>
|
|||
|
|
|||
|
## Solution
|
|||
|
<section id='solution'>
|
|||
|
|
|||
|
```js
|
|||
|
// solution required
|
|||
|
```
|
|||
|
</section>
|