js截取两个字符串之间的内容：     

var str = "aaabbbcccdddeeefff"; 
str = str.match(/aaa(\S*)fff/)[1]; 
alert(str);//结果bbbcccdddeee

js截取某个字符串前面的内容：

var str = "aaabbbcccdddeeefff"; 
tr = str.match(/(\S*)fff/)[1]; 
  alert(str);//结果aaabbbcccddd

js截取某个字符串后面的内容：

var str = "aaabbbcccdddeeefff"; 
str = str.match(/aaa(\S*)/)[1]; 
alert(str);//结果bbbcccdddeeefff

JS利用正则表达式替换字符串中的内容：

//从字符串'Is this all there is'中剪去'is':
  var str='Is this all there is';

  var subStr=new RegExp('is');//创建正则表达式对象
  var result=str.replace(subStr,"");//把'is'替换为空字符串
  console.log(result);//Is th all there is

  var subStr=new RegExp('is','i');//创建正则表达式对象,不区分大小写
  var result=str.replace(subStr,"");//把'is'替换为空字符串
  console.log(result);//this all there is
    
  var subStr=new RegExp('is','ig');//创建正则表达式对象,不区分大小写,全局查找
  var result=str.replace(subStr,"");//把'is'替换为空字符串
  console.log(result);//th all there 

  var subStr=/is/ig;//直接量法创建正则表达式对象,不区分大小写,全局查找
  var result=str.replace(subStr,"");//把'is'替换为空字符串
  console.log(result);//th all there 

  console.log(str);//Is this all there is 可见replace并不改变原始str