使用javascript事件机制限制文本框中只能输入数字

< form >
     < input type = " text "  name = " txt1 "  onkeydown = " checkKey(this) "   />   < br  />
</ form >
< script type = " text/javascript " >
function  checkKey(obj)
... {
    if((event.keyCode >= 48 && event.keyCode <= 57)
        || event.keyCode == 8        //Backspace
        || event.keyCode == 9        //Tab
        || event.keyCode == 35        //End
        || event.keyCode == 36        //Home
        || event.keyCode == 37        //Left
        || event.keyCode == 39        //Right
        || event.keyCode == 190        //.
        )    
    ...{
        if(event.keyCode == 190)
        ...{
            if(obj.value.indexOf('.') >= 0)
                event.returnValue = false;
            else
                event.returnValue = true;
        }
        else
            event.returnValue = true;
    }
    else
    ...{
        event.returnValue = false;
    }
}

</ script >