//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