# Learn JS REGEXP

```javascript
/word/ 匹配整个单词 /word/.test("hello word") 测试字符中是否包含正则匹配，是返回 true,否返回 false "Hello World!".match(/Hello/) 返回 Array [ "Hello" ] /a|b|c/ 匹配 a b c 中的任何一个 /Ww/i 忽略大小写 /word/g 全部匹配 /hu./ 匹配所有以 hu 开头的单词 /[aeiou]/ig 匹配所有符合条件的字母

"Hello World!".match(/[a-z]/gi)

"Hello World123".match(/[a-z0-9]/gi)

/[^{aeiou0}-9]/gi matches all characters that are not a vowel. Note that characters like ., !, [, @, / and white space are matched /^{Amy}/ 匹配开头是 Amy 的字符串 /Amy$/ 匹配结尾是 Amy 的字符串

"Mississippi".match(/s+/g) 不理解，返回 [ 'ss', 'ss' ]

"Aaaaaaa".match(/Aa*/) 返回 Array [ "Aaaaaaa" ]

懒匹配 "<h1>Winter is coming</h1>".match(/<[a-z0-9]*>/)

/\w/g <==> /[A-Za-z0-9_]/g 匹配所有大小写字母、数字、`_` /\W/g 匹配除（大小写字母、数字、`_`）以外的字符

//̣g 匹配所有数字 /\D/g 匹配非数字

/\s/g 匹配全部空格 /§/g 匹配全部非空格

/Oh{3,6}\sno/g.test("Ohhh no")

/Haz{4,}ah/g z 至少重复 4 次

/Tim{4}ber/ m 只重复 4 次

/favou?rite/ 匹配有无 u
```

- caret character (`^`)
- greedy regex (`*C+*`)

## 用户名匹配

<https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/regular-expressions/restrict-possible-usernames>

要求：

1. 用户名只使用字符、数字
2. 唯一的数字必须放在结尾，数字不能作为开头，结尾可以一个/多个数字
3. 字母大小写任意
4. 用户名最短 2 位
5. 如果用户名只有两位，必须全部使用字母

试了几十次，找不到完美通过所有测试的方法：`/^[a-zA-Z][a-zA-Z]̣$/gm`

答案：

1. `/^[a-z][a-z]~~̣$|^[a-z]~~̣̣$/igm`
2. `*^[a-z]([0-9]{2,}|[a-z]+)̣$*`（这一个更加简洁）

## [Positive and Negative Lookahead](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/regular-expressions/positive-and-negative-lookahead)

[freeCodeCamp Challenge Guide: Positive and Negative Lookahead - Guide - The freeCodeCamp Forum](https://forum.freecodecamp.org/t/freecodecamp-challenge-guide-positive-and-negative-lookahead/301360)

如何使用 Positive（`(?`` ...)`） 和 Negative（`(?!...)`） Lookahead？`(? ``\w{6})(?=\w*2̣)`

## [Check For Mixed Grouping of Characters](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/regular-expressions/check-for-mixed-grouping-of-characters)

[freeCodeCamp Challenge Guide: Check For Mixed Grouping of Characters - Guide - The freeCodeCamp Forum](https://forum.freecodecamp.org/t/freecodecamp-challenge-guide-check-for-mixed-grouping-of-characters/301339)

`(Franklin|Eleanor).*\sRoosevelt`

## [Reuse Patterns Using Capture Groups](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/regular-expressions/reuse-patterns-using-capture-groups)

[freeCodeCamp Challenge Guide: Reuse Patterns Using Capture Groups - Guide - The freeCodeCamp Forum](https://forum.freecodecamp.org/t/freecodecamp-challenge-guide-reuse-patterns-using-capture-groups/301364)

`<sup>(+̣)</sup>\s\1\s\1$`

## [Use Capture Groups to Search and Replace](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/regular-expressions/use-capture-groups-to-search-and-replace)

```javascript
let str = 'one two three' let fixRegex = /(\w+)\s(\w+)\s(\w+)/ // Change this line let replaceText = '$3 $2 $1' // Change this line let result = str.replace(fixRegex, replaceText)
```

## [Remove Whitespace from Start and End](https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/regular-expressions/remove-whitespace-from-start-and-end)

[freeCodeCamp Challenge Guide: Remove Whitespace from Start and End - Guide - The freeCodeCamp Forum](https://forum.freecodecamp.org/t/freecodecamp-challenge-guide-remove-whitespace-from-start-and-end/301362)

```javascript
let hello = ' Hello, World! ' let wsRegex = /^\s+|\s+$/g // Change this line let result = hello.replace(wsRegex, '') // Change this line
```

## 工具

1. <https://ihateregex.io/>
2. [Regex Vis](https://regex-vis.com/)


相关：[[js-basics|js-basics]]