----为什么值总是为空(javascript)----

Question

<input value=0123456789 id="txt1"> 
<input type="button" value="getChar" onclick="getCaretPos(txt1)"> 
<script language="javascript"> 
function getCaretPos(obj){ 
obj.focus(); 
var workRange=document.selection.createRange(); 
var allRange=obj.createTextRange(); 
workRange.setEndPoint("StartToStart",allRange); 
len=workRange.text.length; 
alert(obj.value.substr(0,len))
}
</script>

Answer 1

textarea..<textarea id="txt1">0123456789</textarea> 
<input type="button" value="GetChar" onclick="getCaretPos(txt1)"><br> 
<script> 
function getCaretPos(obj) 
{ 
    obj.focus(); 
    var currentRange=document.selection.createRange(); 
    var workRange=currentRange.duplicate(); 
    obj.select(); 
    var allRange=document.selection.createRange(); 
    var len=0; 
    while(workRange.compareEndPoints("StartToStart",allRange)>0) 
    { 
       workRange.moveStart("character",-1); 
       len++; 
    } 
    currentRange.select(); 
    alert(obj.value.substr(0,len)); 
} 
</script>