I want to mark some important points over the curve that gets plotted as shown in the image below. The curve probably does not have data for the interested point.

I read and know that we can annotate a point using plotly-js but that can be done only for the data points that are passed to draw the curve. But how to mark/annotate the point which is not part of data set and data needs to be calculated based on either x/y value passed.