5. 正则 2

用法

1. 可用于字符串匹配
2. 效率高

写法

1. ```javascript
   var reg=/abc/;
   var str=”abcdefg”;
   var result=reg.exec(str);//execute执行
   console.log(result);

   2. ```javascript
      var reg=new RegExp('abc');

{}的作用

匹配数量

var reg=new RegExp('c{2}','g');
console.log(reg.exec("cccccccc"));

匹配手机号

var reg=new RegExp('\\d{3}[0123456789]{8}','g');
console.log(reg.exec("15331860803"));

c{m,n}匹配连续的m到n个(包含m，n)c,如果同时符合，就匹配尽可能多的那个

var reg=/c{3,4}/;
console.log(reg.exec("ccccccc"));

c{m,}匹配大于等于m个c，尽可能找多的

var reg=/c{3,}/;
console.log(reg.exec("cccccccaaaaa"));

[]作用

1. ```javascript
   //划分一个规则集合
   var reg=/[123,]/;
   console.log(reg.exec(“123123,12323”));

   2. ```javascript
      //可以用-来在区间定义多个条件
      var reg=/[a-z]/;
      console.log(reg.exec('Ah'));

*,+,?

*是匹配0个或多个，相当于{0,}

var reg=/c*/;
console.log(reg.exec('cccc'));

+是匹配1个或多个，相当于{1,}

var reg=/c+/;
console.log(reg.exec('ccccaaa'));

?是匹配0个或1个，相当于{0,1}

var reg=/c?/;
console.log(reg.exec('ccccaaa'));

**+,默认贪婪，匹配数量尽可能多，非贪婪模式需要加一个？*

var reg=/c*?/;
console.log(reg.exec('ccccaaa'));//""

^c匹配以c为开始

var reg=/^c/;
console.log(reg.exec('ccccaaa'));//"c"
console.log(reg.exec('accccaaa'));//null

c$匹配以c为结尾

var reg=/c$/;
console.log(reg.exec('cccc'));//"c"
console.log(reg.exec('旺仔小c'));//"c"

.匹配任意字符，只有一个

var reg=/./;
console.log(reg.exec('cccc'));//"c"

var reg=/.+/;
console.log(reg.exec('你好cccc'));//"你好cccc"

var reg=/.{2,3}/;
console.log(reg.exec('你好cccc'));//"你好c"

|或者，优先级高于^

\b是边界的意思,但是遇到中文或者特殊符号会有问题

var reg=/\bc/;
console.log(reg.exec('asd cccc'));//"c"

var reg=/\bc/;
console.log(reg.exec('asdcccc'));//null

var reg=/\bc/;
console.log(reg.exec('asdc'));//null

var reg=/\bc/;
console.log(reg.exec('你好c'));//"c"

var reg=/\bc/;
console.log(reg.exec('c c'));//"c"