求大神给个参考代码，input默认显示数值，点击后自动追加

<html>
<head>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script> 
</head><script type="text/javascript">
</script>
<body>
<input type="text" value="qq.com" id="input" />
<script type="text/javascript">
$(function(){
$("#input").click(function(){

            var obj = document.getElementById("input");
            obj.value = obj.value;
            obj.focus();
            var len = obj.value.length;
            if (document.selection) {
                var sel = obj.createTextRange();
                sel.moveStart('character', 0);
                sel.collapse();
                sel.select();
            } else if (typeof obj.selectionStart == 'number'
&& typeof obj.selectionEnd == 'number') {
                obj.selectionStart = obj.selectionEnd = 0;
            }
})
})
</script>
</body>
</html>