Comparison between class members and configs in ExtJs 4 class model. It seems the configs are diff from members regarding to getter/setter methods created, apply methods created and no straight access to configs (as opposite to members). In addition, members are read-write

gistfile1.js

Ext.define('My.sample.Person', {
    /** @readonly */
    name: 'Unknown',

    config: {
        midname: undefined
    },
    constructor: function(name, config) {
        this.initConfig(config);
        this.name = name;
    },

    eat: function(foodType) {
        console.log(this.name + " is eating: " + foodType);
    },
    
    fullName: function () {
        return this.name +' '+this.getMidname();
    }
});

var aaron = Ext.create('My.sample.Person', 'Aarron', {
    midname: 'Afflalo'
});
    aaron.eat("Salad"); // alert("Aaron is eating: Salad");
console.log('Name for aaron: '+aaron.name);
console.log('Fullname: '+aaron.fullName());
aaron.name = 'Benito';
console.log('New name for aaron: '+aaron.name);