apply(*) pattern

gistfile1.js

applyFoo: function(foo) {
    var currentFooInstance = this.getFoo();

    // If foo config is an instance of Foo class, destroy the current instance (if it exists) and replace with the new one
    if (foo instanceof Foo) {
        if (currentFooInstance) {
            currentFooInstance.destroy();
        }

        currentFooInstance = foo;
    }
    // Otherwise:
    // - If foo is not a valid object, throw an error during development mode
    // - Otherwise:
    //     + If currentFooInstance exists, set the config for it
    //     + Otherwise create a new instance of Foo with that config
    else {
        //<debug error>
        if (!Ext.isObject(foo)) {
            Ext.logger.error("Invalid 'foo' config, must be either an instance of Foo or a config object");
        }
        //</debug>
        if (currentFooInstance) {
            currentFooInstance.setConfig(foo);
        }
        else {
            currentFooInstance = new Foo(foo);
        }
    }

    // currentFooInstance is always a valid instance of Foo here, 
    // and will be assigned to 'this.foo' immediately after this 
    return currentFooInstance;
},