[ksa]

Что-то типа такого

Оно?

function Def() {
	this.mode = "text/html"
	this.tabSize = 2
	this.readOnly = true
};
  
function My_Def() {
	this.readOnly = false
	this.lineWrapping = true
};

var def= new Def();
My_Def.prototype = def;
  
var obj= new My_Def();
for (fld in obj) {
	alert(fld+'='+obj[fld])
};