ExtJS alias vs id

Question

I don't understand the usage of alias vs id vs itemId config properties in ExtJS

app/view/foo.js

Ext.define('app.view.foo', {
    ...
    alias: 'widget.foo',         // 1
    id: 'foo',                   // or 2
    ...
});

app/controller/goo.js

Ext.define('app.controller.goo', {
    ...
    views: ['foo', ...],
    init: function() {
        this.control({
               'foo': {...},     // 1
               '#foo': {...}     // or 2
               ...
        });
        ...
    },
    ...
});

With alias I can use xtype easily.. but what advantage do I gain by setting id's to my views?

Answer 1

An alias is set on the class definition, using Ext.define, and is what is used for the xtype when creating instances (you seem to have the hang of this). An id should be set on a class instance, e.g. when using Ext.create. This just serves as a unique identifier for a particular instance of a component.

FWIW, id should be used sparingly. You are much better served using itemId and referencing components relatively using that, rather than globally with an id.