How to implement dynamic deletion of JavaScript functions _javascript techniques

I am now through the following:
O=odom.createelement ("script");
O.text=document.all.checkrule.value;
ODOM.body.appendChild (o);
You can add a checkrule function,
But I do this code multiple times to insert this checkrule function, so how do I remove the new function first?
Ps:odom represents the Document object for another page, not the document on this page, so typeof (Odom.check_rule) always undefined

ODOM.frames.check_rule = null
Functions with the same name are overwritten.
You can use this ID or name when you add an ID or name to the newly added SCRIPT and then delete it.
But remember, be sure to set the ID or NAME in the CreateElement method

For example: o = document.createelement ("<script language= ' javascript ' id= ' aaa ' >" + "&LT;/SCR" + "ipt>");

Thank you so much.

Synthetic checksum rules
function Docombjs () {
var oeditor = fckeditorapi.getinstance (' FCKeditor1 ');
var ODOM = oeditor.editordocument;
var Elem=odom.getelementbyid ("Checkid");
alert (elem);
if (elem!=null) {
Elem.parentNode.removeChild (Elem);
}
o = Odom.createelement ("<script language= ' javascript ' id= ' Checkid ' >" + "&LT;/SCR" + "ipt>");

O=odom.createelement ("script");
O.text=document.all.checkrule.value;
ODOM.body.appendChild (o);
}
Boss, there's a problem.
If I don't use Odom.createelement ("<script language= ' javascript ' id= ' Checkid ' >" + "&LT;/SCR" + "ipt>"); and directly to write this, I use Var Elem=odom.getelementbyid ("Checkid");
Why get is NULL, must use above createelement, just can find this ID, please help again, thank you!
You mean:

You write <script language= ' javascript ' id= ' Checkid ' ></script&gt directly on the page, but you use the following statement var Elem=odom.getelementbyid (" Checkid "); The object cannot be obtained, is it?