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Extend existing data with NodeJS

Hello everyone!

I am trying to plot a graph with the help of the NodeJS lib: https://github.com/plotly/plotly-nodejs

I have an existing plot which I want to extend daily. I found the fileopt: 'extend' graphOption and it seemed perfect at first, but after I opened the plot in the online Chart Studio, I saw that it created a new grid, copied all the data from the previous grid and added the new data only to the new grid. Luckily, the traces were updated to get their data from the new grid, so after all the plot seemed right.

What is the reason for this strange behaviour? I hoped there was a way to just extend the current grid with the new data. Maybe I’m just not using the API correctly?