js禁用只读文本框获得焦点时的回格键

<script>

document.documentElement.onkeydown = function(evt){
                var b = !!evt, oEvent = evt || window.event;
                if (oEvent.keyCode == 8) {
                var node = b ? oEvent.target : oEvent.srcElement;
                var reg = /^(input|textarea)$/i, regType = /^(text|textarea)$/i;
                if (!reg.test(node.nodeName) || !regType.test(node.type) || node.readOnly || node.disabled) {
                if (b)
                {
                  oEvent.stopPropagation();
                } 
                else 
                {
                    oEvent.cancelBubble = true;
                    oEvent.keyCode = 0;
                    oEvent.returnValue = false;
                }
            }
        }
    }

</script>

脚本来源：http://www.cnblogs.com/troubleLife/archive/2010/04/21/1716904.html