Prototype Examples

gistfile1.js

>>>> Ext.define('Test.view.Explorer', { extend: 'Ext.panel.Panel', showProperties: true, title: 'Properties'});


****** In this case, the String 'My Title' is copied to the object behind foo via Ext.applyIf, because that's what happens with passed config (second param to Ext.create)
>>>> var foo = Ext.create('Test.view.Explorer', {title: 'My Title'}); 
>>>> foo.title;
"My Title"


>>>> var bar = Ext.create('Test.view.Explorer');
******* because title is no property of bar, JS goes up the prototype chain and finds title at bar.constructor.prototype.title (or the deprecated bar.__proto__.title :-)
>>>> bar.title;
"Properties"
******* As Strings are immutable in JS (and every string operation returns a new String), this would be acceptable usage of prototype properties. Objects and Arrays are mutable however, and it's not safe to use them on the prototype. See example below.


>>>> Ext.define('Test.view.NoteExplorer', {extend: 'Test.view.Explorer', title: 'Notes'});

>>>> var notesExplorer = Ext.create('Test.view.NoteExplorer', {title: 'Recent Notes'}); ***** defining title on object notesExplorer via Ext.applyIf
>>>> notesExplorer.title;
****** Found on object, so not going to prototype
"Recent Notes"


>>>> notesExplorer.__proto__.title;
"Notes"

>>>> var notesList = Ext.create('Test.view.NoteExplorer');
>>>> notesList.title;
"Notes"

>>>> foo.title;
"My Title"

>>>> notesExplorer.__proto__.title = 'Hello Motto';
>>>> notesExplorer.title;
"Recent Notes" // still recent notes because we overrode it the subclass
***** it's still "Recent Notes" because it's defined on object notesExplorer, and not looking at prototype at all

>>>> notesList.title;
"Hello Motto" // this traced up the chain to the prototype and used that value

mutable.txt

What you found out is correct, but my point applies to non-primitive/mutable properties on the prototype (Array and Object types), and is in fact not inheritance related. The thing is every object shares a common prototype, even if it's not inheriting something with Ext's class system.

Pratical example in Ext terms:

Ext.define('Explorer', {
    someObjectProperty: {
       title: 'The Explorer'
    }
});
var oneExplorer=Ext.create('Explorer');
var twoExplorer=Ext.create('Explorer');
oneExplorer.someObjectProperty.title = 'One explorer' // *1)
"One explorer"
oneExplorer.someObjectProperty.title
"One explorer" // that was expected
twoExplorer.someObjectProperty.title
"One explorer" // that was probably *not* intended. We only changed the title on oneExplorer, and not twoExplorer, so it should be 'The Explorer', right ;-)

*1) someObjectProperty not found on object, so proto property is fetched on first '.' operator. The second '.' operator operates on proto property, fetching reference to title. The = operator changes the title reference from the String 'The Explorer', to the String 'One explorer'. **The someObjectProperty is still on the prototype, and shared between all objects with the changed title attribute**