ExtJS 6: Should I use the config object?

Question

I'm building an application with ExtJS 6. I've already read the guides, tutorials and best practice tips. But what I dont understand yet is, why should I use the config object?

With config:

Ext.define('MyProject.foo.Bar', {
    extends: 'Ext.window.Window',

    ...

    config: {
        title: 'My title'
    }
});

Without config:

Ext.define('MyProject.foo.Bar', {
    extends: 'Ext.window.Window',

    ...

    title: 'My title'
});

Both are working as expected. Can anyone tell me the difference and possible benefits?

Answer 1

It's all described in the Class System guide:

• Configurations are completely encapsulated from other class members
• Getter and setter methods for every config property are automatically generated into the class prototype during class creation if methods are not already defined.
• The auto-generated setter method calls the apply method (if defined on the class) internally before setting the value. You may override the apply method for a config property if you need to run custom logic before setting the value. If your apply method does not return a value, the setter will not set the value. The update method (if defined) will also be called when a different value is set. Both the apply and update methods are passed the new value and the old value as params.