JavaScript binding loss with setTimeout
The problem is that this._slideIn refers to a function, not a method invocation.  In your third code sample, changing your last line to

var self = this;
setTimeout(function() { self._slideIn(componentId) }, 20);


should be sufficient.  You have to capture this in the closure that you pass to setTimeout(), because when the code runs later, this will refer to something else in that execution context.