static/ext/src/class/Base.js
function(config) {
            var instanceConfig = config,
                configNameCache = Ext.Class.configNameCache,
                defaultConfig = new this.configClass(),
                defaultConfigList = this.initConfigList,
                hasConfig = this.configMap,
                nameMap, i, ln, name, initializedName;

            this.initConfig = Ext.emptyFn;

            this.initialConfig = instanceConfig || {};

            this.config = config = (instanceConfig) ? Ext.merge(defaultConfig, config) : defaultConfig;

            if (instanceConfig) {
                defaultConfigList = defaultConfigList.slice();

                for (name in instanceConfig) {
                    if (hasConfig[name]) {
                        if (instanceConfig[name] !== null) {
                            defaultConfigList.push(name);
                            this[configNameCache[name].initialized] = false;
                        }
                    }
                }
            }

            for (i = 0,ln = defaultConfigList.length; i < ln; i++) {
                name = defaultConfigList[i];
                nameMap = configNameCache[name];
                initializedName = nameMap.initialized;

                if (!this[initializedName]) {
                    this[initializedName] = true;
                    this[nameMap.set].call(this, config[name]);
                }
            }

            return this;
        }
function(config) {
            var instanceConfig = config,
                configNameCache = Ext.Class.configNameCache,
                defaultConfig = new this.configClass(),
                defaultConfigList = this.initConfigList,
                hasConfig = this.configMap,
                nameMap, i, ln, name, initializedName;

            this.initConfig = Ext.emptyFn;

            this.initialConfig = instanceConfig || {};

            this.config = config = (instanceConfig) ? Ext.merge(defaultConfig, config) : defaultConfig;

            if (instanceConfig) {
                defaultConfigList = defaultConfigList.slice();

                for (name in instanceConfig) {
                    if (hasConfig[name]) {
                        if (instanceConfig[name] !== null) {
                            defaultConfigList.push(name);
                            this[configNameCache[name].initialized] = false;
                        }
                    }
                }
            }

            for (i = 0,ln = defaultConfigList.length; i < ln; i++) {
                name = defaultConfigList[i];
                nameMap = configNameCache[name];
                initializedName = nameMap.initialized;

                if (!this[initializedName]) {
                    this[initializedName] = true;
                    this[nameMap.set].call(this, config[name]);
                }
            }

            return this;
        }
<feature classSystem.config> 
Initialize configuration for this class. a typical example:

Ext.define('My.awesome.Class', {
// The default config
config: {
name: 'Awesome',
isAwesome: true
},

constructor: function(config) {
this.initConfig(config);
}
});

var awesome = new My.awesome.Class({
name: 'Super Awesome'
});

alert(awesome.getName()); // 'Super Awesome'

@protected
@param {Object} config
@return {Ext.Base} this