jsss

function verify() {

var val = $('amount').value;

var reg = /^([1-9][0-9]*|0)(\.[0-9]+)?$/;

if (reg.test(val)) {

alert('很合法');

} else {

alert('不合法');

}

}
<script>
//选中文本中指定部分
var set_caret_position = function(obj,start,end){
   if(document.selection){
    if(obj.tagName=='TEXTAREA'){
     var i=obj.value.indexOf("\r",0);
     while(i!=-1&&i<end){
      end--;
      if(i<start){
       start--;
      }
      i=obj.value.indexOf("\r",i+1);
     }
    }
    var range=obj.createTextRange();
    range.collapse(true);
    range.moveStart('character',start);
    if(end!=undefined){
     range.moveEnd('character',end-start);
    }
    range.select();
   }else{
    obj.selectionStart=start;
    var sel_end=end==undefined?start:end;
    obj.selectionEnd=Math.min(sel_end,obj.value.length);
    obj.focus();
   }
};
alert("tes".length);
alert("特殊".length);
</script>


<textarea name="yourForm" id="yourForm" rows=3 cols=40 wrap=virtual>这里是测试文本......</textarea><BR> 

<input type=button value="选中所有内容" onClick="set_caret_position(document.getElementById('yourForm'),3,9)"><BR>


<script>
//选中文本中指定部分
function set_caret_position(obj){
var objVal = "abcdefg";
var val = obj.value;
var end = objVal.length;
var start = val.length;
if (objVal.substr(0,start) == val) {
obj.value = objVal;
if(document.selection){
    var range=obj.createTextRange();
    range.collapse(true);
    range.moveStart('character',start);
    range.moveEnd('character',end);
    range.select();
   }else{
    obj.selectionStart=start;
    obj.selectionEnd=end;
    obj.focus();
   }
}
};
</script>
<input type="text" id="yourForm" value="" onkeyup="set_caret_position(this)"/><BR>