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Private methods are methods that start with an underscore. They are expected to be accessed directly using the this keyword. Private methods are common and recommended.
This implies that there is a considerable overhead, for widgets with a lot of code that have multiple instances, in having the heavy-lifting functions implemented as private methods.For each of the options that changes the DOM, we call a specific helper method. The helper methods, createBars, createMarkers and createTickBar are specified outside of the widget instance properties. This is because they are the same for all widgets and need not be created individually for each widget instance.