<input type="text" value="TEST" id="demo" />
<script type="text/javascript">
document.getElementById('demo').onkeydown = function() { return false; }
</script>

------解决方案--------------------
试试这样：
HTML code
window.onload=function(){
    var testInput = document.getElementById('test');
    testInput.onkeyup = function() {
        this.value=this.value.replace(/[\s\S]/g,'');
        //stopDefault(e);
    }
}
</script>
<form name="formA" method="post"  >
<input type=text name="a" id="test" >
<form>

------解决方案--------------------
设置文本框只读,或者不可用.
<input   type= "text "   name= "test "   readonly>

OR

<input   type= "text "   name= "test "   disabled>

------解决方案--------------------
不能输入的话 你绑定onkeydown事件好了