How to append additional data to node and access them at then javascript?

I want add some additional data to the node and access the data when click it.The additional data isn’t display in the node object.

Sure, add whatever properties that you need to the node data object. http://gojs.net/latest/intro/usingModels.html

This describes the click event handler and how to get to the node’s data: http://gojs.net/latest/api/symbols/GraphObject.html#click