入门JavaScript正则表达式

概念

regular expression,描述了一种字符串匹配的模式(pattern),可以用来检查一个串是否含有某种子串、将匹配的子串替换或者从某个串中取出符合某个条件的子串等。

正则表达式的创建

字面量创建

let str = "abc1231dfaf123213fda";
let reg = /\d+/g;
let res = str.match(reg);
console.log(res); // ["1231", "123213"]

构造函数创建

正则支持变量拼接,对于特殊字符需要加\转义

let str = "abc1231dfaf123213fda";
let reg = new RegExp("\\d+", "g");
let res = str.match(reg);
console.log(res); // ["1231", "123213"]

测试链接:https://jsbin.com/sivoqayowo/edit?js,console,output


正则的匹配方法

正则对象底下的方法:test,exec

注意lastIndex属性,它决定下一次匹配从什么地方开始

// test
let str = "abc1231dfaf123213fda";
let reg = /\d+/g;
console.log(reg.test(str) +":"+ reg.lastIndex); // "true:7"
console.log(reg.test(str) +":"+ reg.lastIndex); // "true:17"
console.log(reg.test(str) +":"+ reg.lastIndex); // "false:0"
// exec
let str0 = "abc1231dfaf123213fda";
let reg0 = /\d+/g;
console.log(reg0.exec(str0) +":"+ reg0.lastIndex); // "1231:7"
console.log(reg0.exec(str0) +":"+ reg0.lastIndex); // "123213:17"
console.log(reg0.exec(str0) +":"+ reg0.lastIndex); // "null:0"

测试链接:https://jsbin.com/taloyiwuba/edit?js,console,output

字符串底下的方法:split,search,match,replace

// split
let str = "abc1231dfaf123213fda";
let reg = /\d+/g;
let arr = str.split(reg);
console.log(arr); // ["abc", "dfaf", "fda"]
// search 会忽略全局匹配g
let str0 = "abc1231dfaf123213fda";
let reg0 = /\d+/g;
console.log(str.search(reg0)); // 3
console.log(str.search(reg0)); // 3
// match
let str1 = "abc1231dfaf123213fda";
let reg1 = /\d+/g;
console.log(str1.match(reg1)); // ["1231", "123213"]
// replace 第二个参数支持字符串和函数二种方法,函数较灵活,可以实现很多高级功能
let str2 = "abc3dfaf2fda";
let reg2 = /\d/g;
let result20 = str2.replace(reg2,'*');
console.log(result20); // "abc*dfaf*fda"
let result21 = str2.replace(reg2,function(...args) {
  // args是一个数组['匹配到的值','索引','分组','原始字符串']
  console.log(args);
	// ["3", 3, "abc3dfaf2fda"]
	// ["2", 8, "abc3dfaf2fda"]
  return "*";
});
console.log(result21); // "abc*dfaf*fda"

测试链接:https://jsbin.com/pozoxibiwi/edit?js,console,output


元字符

正则表达式中有特殊含义的非字母字符

字符相关:

  • \w:数字 字母 下划线
  • \W:非数字 字母 下划线
  • \d:数字
  • \D:非数字
  • \s:匹配一个空白符,包括空格、制表符、换页符、换行符和其他 Unicode 空格
  • \S:匹配一个非空白符
  • . :匹配行结束符(\n \r \u2028 或 \u2029)以外的任意单个字符
  • \:转义符
    • 表示下一个具有特殊含义的字符为字面值
    • 表示下一个字符具有特殊含义(转义后的结果是元字符内约定的)
// \w
let str00 = "1234_abc";
let str01 = "~%$*";
console.log('\\w:0--' + /\w+/g.test(str00)); // "\w:0--true"
console.log('\\w:1--' + /\w+/g.test(str01)); // "\w:1--false"

// \W
let str10 = "1234_abc";
let str11 = "~%$*";
console.log('\\W:0--' + /\W+/g.test(str10)); // "\W:0--false"
console.log('\\W:1--' + /\W+/g.test(str11)); // "\W:1--true"

// \s
let str20 = "1234 abc";
let str21 = "1234abc";
console.log('\\s:0--' + /\s+/g.test(str20)); // "\s:0--true"
console.log('\\s:1--' + /\s+/g.test(str21)); // "\s:1--false"

// \S
let str30 = " ";
let str31 = "1234abc";
console.log('\\S:0--' + /\S/g.test(str30)); // "\S:0--false"
console.log('\\S:1--' + /\S/g.test(str31)); // "\S:1--true"

// \d
let str40 = "1234abc";
let str41 = "abc";
console.log('\\d:0--' + /\d+/g.test(str40)); // "\d:0--true"
console.log('\\d:1--' + /\d+/g.test(str41)); // "\d:1--false"

// \D
let str50 = "1234";
let str51 = "abc";
console.log('\\D:0--' + /\D+/g.test(str50)); // "\D:0--false"
console.log('\\D:1--' + /\D+/g.test(str51)); // "\D:1--true"

// .
let str60 = "1234";
let str61 = "\r\n";
console.log('.:0--' + /.+/g.test(str60)); // "\D:0--true"
console.log('.:1--' + /.+/g.test(str61)); // "\D:1--false"

测试链接:https://jsbin.com/yajepuyeni/edit?js,console,output

数量相关:

  • {}:出现次数控制
    • {n,m} 出现n次到m次
    • {n} 出现n次
    • {n, } 至少出现n次
  • ?: 出现0次或1次,还有另一个用处就是贪婪和惰性匹配
  • +:出现1次或多次
  • *: 出现0次或多次
let str = "aeeef";
let reg = /e{3}/;
let reg0 = /e{1,3}/
let reg1 = /e{4,}/
console.log(reg.test(str)); // true
console.log(reg0.test(str)); // true
console.log(reg1.test(str)); // false

let reg2 = /aa?e/;
console.log(reg2.test(str)); // true

let str0 = "123456789";
let reg3 = /\d{2,4}/g;
let reg4 = /\d{2,4}?/g;
console.log(str0.match(reg3)); // ["1234", "5678"]
console.log(str0.match(reg4)); // ["12", "34", "56", "78"]

let reg5 = /ae+/;
console.log(reg5.test(str)); // true

let reg6 = /ae*f/;
console.log(reg6.test(str)); // true

测试链接:https://jsbin.com/hirobabico/edit?js,console,output

位置相关:

  • ^:开始位置,在[]中是取反的意思
  • $:结尾置
  • \b:边界位置(空格,开头,结尾等非\w的都是边界)
  • \B:非边界位置
let str = "this is a book";
let reg = /^\w/g;
console.log(str.replace(reg, "*")); // "*his is a book"

let reg3 = /[^is]/g;
console.log(str.replace(reg3, "*")); // "**is*is*******"

let reg0 = /\w$/g;
console.log(str.replace(reg0, "*")); // "this is a boo*"

let reg1 = /\bis\b/g;
console.log(str.replace(reg1, "*")); // "this * a book"

let reg2 = /\Bis\b/g;
console.log(str.replace(reg2, "*")); // "th* is a book"

测试地址:https://jsbin.com/camopiduye/edit?js,console,output

括号相关:

  • ():分组、提取值,替换,反向引用
let str = "abababdgdgdg";
// 分组
let reg = /(ab){3}/;
console.log(reg.test(str)); // true

let str0 = "2021-11-24";
let reg0 = /(\d{4})-(\d{2})-(\d{2})/;
// 提取值
console.log(str0.match(reg0)); // ["2021-11-24", "2021", "11", "24"]
console.log(RegExp.$1 +":"+ RegExp.$2 +":"+ RegExp.$3); // "2021:11:24"

// 替换
console.log(str0.replace(reg0, "$2/$3/$1")) // "11/24/2021"

let strReplace = str0.replace(reg0, function(...args) {
  console.log(args); // ["2021-11-24", "2021", "11", "24", 0, "2021-11-24"]
  return args[2] + "/" + args[3]  + "/" + args[1];
})
console.log(strReplace); // "11/24/2021"

// 反向引用
let className = "main-content-left";
let reg1 = /\w+(-|_)\w+(-|_)\w+/;
console.log(reg1.test(className)); // true
let className0 = "main-content_left";
// 只有前后要么都是-要么都是_才符合要求
let reg2 = /\w+(-|_)\w+(\1)\w+/;
console.log(reg2.test(className0)); // false

测试链接:https://jsbin.com/woliqaxoto/edit?js,console,output

  • []:字符集合
let str = "my name is limili";
let reg = /li[mi]*li/g;
console.log(reg.test(str)); // true

let str0 = "sdf566dfdfdr";
// 支持定义一个范围,按ASCII顺序
let reg0 = /[0-9]/g;
let reg1 = /[a-z]/g;
console.log(reg0.test(str0)); // true
console.log(reg1.test(str0)); // true

// 中括号中的^是取反的意思
let reg2 = /[^a-z]/g;
console.log(str0.replace(reg2, "*")); // "sdf***dfdfdr"

测试链接:https://jsbin.com/gosenezuvo/edit?js,console,output

  • {}:出现次数控制,参考前面数量相关

匹配模式

  • g:全局匹配
  • i:忽略大小写
  • m:多行匹配
  • s:让“.”可以匹配换行符
  • u:让正则可以匹配unicode编码
  • y:粘性匹配模式
// g 全局匹配
let str = "15fdfdf2dfd5df2";
let reg = /\d+/;
let reg0 = /\d+/g;
console.log(str.match(reg)); // ["15"]
console.log(str.match(reg0)); // ["15", "2", "5", "2"]

// i 忽略大小写
let str0 = "AbC";
let reg1 = /abc/i;
console.log(reg0.test(str0)); // false

// m 支持多行匹配
let str1 =`abc
def
hij`;

let reg2 = /^\w/g;
console.log(str1.replace(reg2, "*")); 
// "*bc
// def
// hij"

let reg3 = /^\w/gm;
console.log(str1.replace(reg3, "*"));
// "*bc
// *ef
// *ij"

// s 让"."号可以匹配换行符
let reg4 = /a.+j/g;
console.log(reg4.test(str1)); // false
let reg5 = /a.+j/gs;
console.log(reg5.test(str1)); // true

// u 匹配unicode编码
let str2 = "a";
let reg6 = /\u{61}/;
console.log(reg6.test(str2)); // false
let reg7 = /\u{61}/u;
console.log(reg7.test(str2)); // true

// y 粘性匹配
let str3 = "12d3c4";
let reg8 = /\d/g;
console.log(reg8.exec(str3)); // ["1"]
console.log(reg8.exec(str3)); // ["2"]
console.log(reg8.exec(str3)); // ["3"]
let reg9 = /\d/gy;
console.log(reg9.exec(str3)); // ["1"]
console.log(reg9.exec(str3)); // ["2"]
console.log(reg9.exec(str3)); // null

测试链接:https://jsbin.com/lafimibeqi/edit?js,console,output

命名分组

通过“?<组名>”定义命名分组

let str = "2021-11-24";
let reg = /(\d+)-(\d+)-(\d+)/;
console.log(str.match(reg));
// {
// 	0: "2021-11-24"
// 	1: "2021"
// 	2: "11"
// 	3: "24"
// 	groups: undefined
// 	index: 0
// 	input: "2021-11-24"
// }
let reg0 = /(?\d+)-(?\d+)-(?\d+)/;
console.log(str.match(reg0));
// {
// 	0: "2021-11-24"
// 	1: "2021"
// 	2: "11"
// 	3: "24"
// 	groups: {y: "2021", m: "11", d: "24"}
// 	index: 0
// 	input: "2021-11-24"
// }

测试链接:https://jsbin.com/tosameyadi/edit?js,output,打开控制台看日志

零宽断言

  • ?=:正向肯定零宽断言
  • ?!:正向否定零宽断言
  • ?>=:负向零宽肯定断言
  • ?
let str = "iphone4iphone5iphonex";
let reg = /iphone\d/g;
console.log(str.replace(reg, "苹果")); // "苹果苹果iphonex"
let reg0 = /iphone(?=\d)/g;
console.log(str.replace(reg0, "苹果")); // "苹果4苹果5iphonex"

let reg1 = /iphone(?!\d)/g;
console.log(str.replace(reg1, "苹果")); // "iphone4iphone5苹果x"

let str0 ="100px200px10rpx";
let reg2 = /(?<=\d+)px/g;
console.log(str0.replace(reg2, "像素")); // "100像素200像素10rpx"
let reg3 = /(?

测试链接:https://jsbin.com/nerenuyose/edit?js,console,output

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