Need additon to this script to set text fields to read only.

I currently using this javascript to timestamp a date field upon signing. However, I cannot also check the other box in the selection that will make fields read only. Therefore, what is the javascript command that sets fields to read only, and how would i add it to this script?

var f=this.getField("CURRENTDATE");{
f.value = (new Date()).toString();
AFDate_FormatEx("h:MM tt, mmm dd, yyyy");
}