AppendChild and createElement usage in JS

The original js Code is:
Var theform = document. forms [0];
Theform. appendChild (document. createElement ("<input type = 'den den 'name = '_ EVENTTARGET'> "));
This is useful in IE, but Firefox does not.
Take document. createElement ("<input type = 'den den 'name = '_ EVENTTARGET'>") and test it. It is found that there is an error in this line.
Message: String contains an invalid character "code:" 5
I found on the Internet that Firefox uses document. createElement (option). Note: What I need is input, so:
Var options = document. createElement ("input ");
Options. setAttribute ("name", "_ EVENTARGUMENT ");
Options. setAttribute ("type", "hidden ");
Theform. appendChild (options );
Firefox and IE are not easy to use, or: String contains an invalid character "code:" 5
Refer to the code called below
Theform. _ eventtarget. value = eventtarget. Split ("$"). Join (":");
Theform. _ eventargument. value = eventargument;
Consider whether an ID is required:
VaR Options = Document. createelement ("input ");
Options. setattribute ("name", "_ eventargument ");
Options. setattribute ("ID", "_ eventargument ");
Options. setattribute ("type", "hidden ");
Theform. appendchild (options );

Really easy to use!