error in javascript when creating command dialog

[Cuckoo]

when I create a command dialog as a dreamweaver extension, the "readonly"
attribute of either textarea or input are not working. is there any method i
can use to set the input box readonly, instead of setting the "disable"
attribute?

Moreover not all the javascript can work. eg: <input type="text"
onkeydown="return false;" onfocus="blur();"/>
It will prompt error with message: While executing onKeyDown in xxx.htm, a
JavaScript error occurred.
Is there any ways I can fix it?

Thanks a lot