var comm={
                getPositionForInput:function(ctrl){ //普通文本框
                    var CaretPos = 0; 
                    if (document.selection) { // IE Support 
                        ctrl.focus(); 
                        var Sel = document.selection.createRange(); 
                        Sel.moveStart('character', -ctrl.value.length); 
                        CaretPos = Sel.text.length; 
                    }else if(ctrl.selectionStart || ctrl.selectionStart == '0'){// Firefox support 
                        CaretPos = ctrl.selectionStart; 
                    } 
                        return (CaretPos); 
                }, 
                getPositionForTextArea:function(ctrl) { //多行文本框
                    var CaretPos = 0; 
                    if(document.selection) {// IE Support 
                        ctrl.focus(); 
                        var Sel = document.selection.createRange(); 
                        var Sel2 = Sel.duplicate(); 
                        Sel2.moveToElementText(ctrl); 
                        var CaretPos = -1; 
                        while(Sel2.inRange(Sel)){ 
                        Sel2.moveStart('character'); 
                        CaretPos++; 
                        } 
                    }else if(ctrl.selectionStart || ctrl.selectionStart == '0'){// Firefox support 
                        CaretPos = ctrl.selectionStart; 
                    } 
                    return (CaretPos); 
                }, 
                setCursorPosition:function(ctrl, pos){ //设置光标位置函数 
                    if(ctrl.setSelectionRange){ 
                        ctrl.focus(); 
                        ctrl.setSelectionRange(pos,pos); 
                    }else if (ctrl.createTextRange) { 
                        var range = ctrl.createTextRange(); 
                        range.collapse(true); 
                        range.moveEnd('character', pos); 
                        range.moveStart('character', pos); 
                        range.select(); 
                    } 
                }, 
                getStrLength:function(str){
                    return str.length;
                },
                process:function( id,targetId ){ //test
                    var no = document.getElementById(id).value; 
                    setCursorPosition(document.getElementById(targetId),no); 
                } 
            }


 使用方法：



<body> 
<div class="title">JavaScript 获取/设置光标位置,兼容Input&&TextArea：</div> 
<div class="title">单行文本框</div> 
<p><input class="input" id="textbox" name="textbox" value="Hi,www.jb51.net!!!" /></p> 

<input type="button" onclick="alert( getPositionForInput( document.getElementById('textbox') ) )" value="Get Position"> 
输入位置: <input type="text" id="no1" size="1" /><input type="button" onclick="process('no1','textbox');" value="Set Position"> 

<div class="title">多行文本框</div> 
<textarea id="zhangdanNum" name="zhangdanNum" style="height:66px;width:246px;overflow:hidden">Hi,CssRain!!!</textarea> 
<input type="button" onclick="alert( getPositionForTextArea( document.getElementById('zhangdanNum') ) )" value="Get Position"> 
输入位置: <input type="text" id="no2" size="1" /><input type="button" onclick="process('no2','zhangdanNum');" value="Set Position"> 
</body>