正则捕获与test方法

正则捕获的方法

前面介绍了exec和match的正则捕获；本节进行总结正则的捕获； - exec - test

• 字符串 String.prototype 上支持正则表达式处理的方式
  • replace
  • match
  • splite

test 捕获

test 默认只能验证，是true还是false;

let str = "axihe2020an06bang30";
let reg = /\d+/g;
console.log(reg.test(str));//true

还记得上面说test可以改变reg.lastIndex么？

test 捕获就是运用这个思路的

let str = "axihe2020an06bang30";
let reg = /(\d+)/g;
console.log(reg.test(str));//true
console.log(RegExp.$1);//"2020"
console.log(RegExp.$2);//""
console.log(RegExp.$3);//""
console.log(RegExp.$4);//""

我们发现RegExp.$1有值，但是其它的都没有值了，我们再试试多次捕获。

let str = "axihe2020an06bang30";
let reg = /(\d+)/g;
console.log(`lastIndex:${reg.lastIndex}`);//
console.log(reg.test(str));//true
console.log(`lastIndex:${reg.lastIndex}`);//
console.log(`$1:${RegExp.$1}`);//"2020"
console.log(`$2:${RegExp.$2}`);//""
console.log(`$3:${RegExp.$3}`);//""
console.log(`\n`);
console.log(reg.test(str));//true
console.log(`lastIndex:${reg.lastIndex}`);//
console.log(`$1:${RegExp.$1}`);//"06"
console.log(`$2:${RegExp.$2}`);//""
console.log(`$3:${RegExp.$3}`);//""
console.log(`\n`);
console.log(reg.test(str));//true
console.log(`lastIndex:${reg.lastIndex}`);//
console.log(`$1:${RegExp.$1}`);//"30"
console.log(`$2:${RegExp.$2}`);//""
console.log(`$3:${RegExp.$3}`);//""
console.log(`\n`);
console.log(reg.test(str));//true
console.log(`lastIndex:${reg.lastIndex}`);//
console.log(`$1:${RegExp.$1}`);//"30"
console.log(`$2:${RegExp.$2}`);//""
console.log(`$3:${RegExp.$3}`);//""
console.log(`\n`);
console.log(reg.test(str));//true
console.log(`lastIndex:${reg.lastIndex}`);//
console.log(`$1:${RegExp.$1}`);//"2020"
console.log(`$2:${RegExp.$2}`);//""
console.log(`$3:${RegExp.$3}`);//""
console.log(`\n`);
console.log(reg.test(str));//true
console.log(`lastIndex:${reg.lastIndex}`);//
console.log(`$1:${RegExp.$1}`);//"06"
console.log(`$2:${RegExp.$2}`);//""
console.log(`$3:${RegExp.$3}`);//""
console.log(`\n`);
console.log(reg.test(str));//true
console.log(`lastIndex:${reg.lastIndex}`);//
console.log(`$1:${RegExp.$1}`);//"30"
console.log(`$2:${RegExp.$2}`);//""
console.log(`$3:${RegExp.$3}`);//""
console.log(`\n`);
console.log(reg.test(str));//true
console.log(`lastIndex:${reg.lastIndex}`);//
console.log(`$1:${RegExp.$1}`);//"30"
console.log(`$2:${RegExp.$2}`);//""
console.log(`$3:${RegExp.$3}`);//""

总结：RegExp.$1–RegExp.$9储存当前本次正则匹配后，第一个到第九个分组的信息；

更多的信息可以看console.dir(RegExp)

let str = "axihe2020an06bang30";
let reg = /(\d+)/g;
console.log(`lastIndex:${reg.lastIndex}`);//
console.log(reg.test(str));//true
console.log(`lastIndex:${reg.lastIndex}`);//
console.log(`$1:${RegExp.$1}`);//"2020"
console.dir(RegExp);
console.log(`\n`);
console.log(reg.test(str));//true
console.log(`lastIndex: ${reg.lastIndex}`);//
console.log(`$1: ${RegExp.$1}`);//"06"
console.dir(RegExp);

为甚会出现两次"30"呢？作为思考