What code should I use to plot a graph of a dragged range in a spreadsheet?

[decomposition502]

I would like to read an xlsx file in a browser, display its contents on a spreadsheet, and plot the array values of the dragged range on a graph in the spreadsheet, but I don't know how to code it.

I can tell which range I dragged by using the Selection event, but I can't think of a way to implement it so that the index values for that range are taken out of the function and used to plot the graph.

I'm a Javascript novice, so please, be polite. Thank you in advance.