正则的捕获组

 var text = "this has been a short summer";
 var pattern = /(..)or(.)/g;
  if (pattern.test(text)){
      alert(RegExp.$1);       //sh
      alert(RegExp.$2);       //t
  }

如上代码意思为找到'or'字符串,$1为匹配处的前两位字符，$2为匹配处的后1位字符

var text = "this has been a short summer";
var pattern = /(.*)as(.*)or(.*)/g;
if (pattern.test(text)){
    alert(RegExp.$1);       //this h
    alert(RegExp.$2);       // been a sh
    alert(RegExp.$3);      //t summer
}

var text = "this has been a short summer";
var pattern = /(.)hort/g;
 if (pattern.test(text)){
    alert(RegExp.input); // this has been a short summer
    alert(RegExp.leftContext);// this has been a
    alert(RegExp.rightContext);//  summer
    alert(RegExp.lastMatch);// short
    alert(RegExp.lastParen);// s
    alert(RegExp.multiline);// false
}

• input属性返回原始字符串
• leftContext属性返回了单词short之前的字符串, 而rightContext返回了单词short之后的字符串
• lastMatch属性返回最近一次与整个正则表达式匹配的字符串，即short
• lastParen属性返回最近一次匹配的捕获组，即s
  等同于

if (pattern.test(text)){
    alert(RegExp.$_);// this has been a short summer
    alert(RegExp["$`"]);// this has been a
    alert(RegExp["$'"]);//  summer
    alert(RegExp["$&"]);// short
    alert(RegExp["$+"]);// s
    alert(RegExp["$*"]);// false