Helper in lightning bundle is similar to controller where you write client-side javascript methods. These methods are more like reuseable methods which can be called from any controller method.
- Helper is similar to controller but helper does not handle events.
- Helper can be used to write reusable Javascript methods and these can be called from Controller section.
- Helper functions also enable specialization of tasks, such as processing data and queueing server-side actions.
- Helper methods are local to Component bundle.
- Helper methods can be called from any controller javascript methods.
- Declaring a helper method is similar to controller javascript method.
- A helper function can pass in any arguments required by the function, such as the component it belongs to, a callback, or any other objects.
- You can call a helper method from another helper method using this. operation.
Akhil Kulkarni 