ES9-正则扩展

命名捕获分组

 let str = '<a href="http://www/atguigu.com">尚硅谷</a>';

        // 1.
        const reg = /<a href="(.*)">(.*)<\/a>/;
        const result = reg.exec(str);
        // console.log(result);
        /* 
        [ "<a href=\"http://www/atguigu.com\">尚硅谷</a>", "http://www/atguigu.com", "尚硅谷" ]
0: "<a href=\"http://www/atguigu.com\">尚硅谷</a>"

1: "http://www/atguigu.com"

2: "尚硅谷"]
         */

         const reg1 = /<a href="(?<url>.*)">(?<text>.*)<\/a>/;
        const result1 = reg1.exec(str);
        console.log(result1);
        /*
        [ "<a href=\"http://www/atguigu.com\">尚硅谷</a>", "http://www/atguigu.com", "尚硅谷" ]
0: "<a href=\"http://www/atguigu.com\">尚硅谷</a>"

1: "http://www/atguigu.com"

2: "尚硅谷"]

//–––––––––––––– groups有值
groups: Object { url: "http://www/atguigu.com", text: "尚硅谷" }
         */

正向断言 反向断言

 let str = "jseee你知道呢555啦啦啦";
        // 正向断言
        const reg = /\d+(?=啦)/;
        const result = reg.exec(str);
        console.log(result);
        /* 
        Array [ "555" ]
0: "555"
groups: undefined
index: 9
input: "jseee你知道呢555啦啦啦"
length: 1
         */


        // 反向断言
        const reg1 = /(?<=呢)\d+/;
        const result1 = reg.exec(str);
        console.log(result1);
                /* 
        Array [ "555" ]
0: "555"
groups: undefined
index: 9
input: "jseee你知道呢555啦啦啦"
length: 1
         */