preRender(config, logger, processor, el)
Occurs right before the chart starts rendering. You can modify the configuration in this handler.
config is a configuration object that will be used to render the chart. Supported types:
logger is a Logger instance.
processor is the chart builder which is currently processing your data.
el is a jQuery object wrapping an HTML-container where the chart will be rendered.
Returns Deferred, Promise, or other object.
If you need to call an asynchronous operation, you can return a Deferred or Promise object and resolve it when the operation completes.