正则表达式1

 $ 表示寻找指定字符串的结尾的位置， 表示单词的边界例如：

 var reg4=/are$/g;
   var reg5=/are/g;

   var str="we are thinking that      that cars      are";
   console.log(str.match(reg4)); //["are"]
   console.log(str.match(reg5));  //["are", "are"]

　

　　反向引用查找重复的单词：

 var reg3=/([A-Za-z]+)s+1/g;
   var str="we are thinking that      that cars      are";
   console.log(str.match(reg3)); //["that      that"]