两个JS对象怎样才能相等

在JS中，两个对象如何才能相等？下面的两个 Alert，只有一个输出true. 在JS中如何才能构造出两个JS对象相等？

var PRop1 = {asd:{def:'abc'}};

var prop2 = {asd:{def:'abc'}}; alert( prop1==prop2)//false alert( prop1['asd']==prop2['asd'] ) ;//false

alert( prop1['asd']['def']==prop1['asd']['def'] ) ; //true

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD> <TITLE> New Document </TITLE>

var prop1 = {asd:{def:'abc'}};

var prop2 = {asd:{def:'abc'}}; alert( prop1==prop2)//false alert( prop1['asd']==prop2['asd'] ) ;//false

alert( prop1['asd']['def']==prop1['asd']['def'] ) ; //true

</script>

</HEAD>

<BODY>

</BODY> </HTML>