<script>
function replacestr(str,re)
{
var reg=new RegExp(re,"g")
var nstr;
str = str.replace(reg,function($1,$2){
        if($2!="")
        {
            return "lai";
        }
        if($1!=""){
            return "nihao";
        }
    });
    alert(str)
}
var str="a123测试abc" ;
var re ="([a-z]+)|(\d+)";
replacestr(str,re)
</script>

<script language="javascript"   runat=server>
function replacestr1(str,re)
{
var reg=new RegExp(re,"g")
str = str.replace(reg,function($1,$2){
        if($2!="") { return "lai";
        }
        if($1!=""){
            return "nihao";
        }
    });
    return str
}
</script>