Histogram counts in bin under mouse hover

I would like to make a histogram, under IJulia jupyter notebook, such that, when I hover the mouse over the bars, I get the number of ocurrences within the corresponding bins, as a tooltip. My MWE is:

using PlotlyJS
df = DataFrame(a=[1, 2, 2, 3, 2, 0, 2, 4, 4])

which does show the plot, but without any tooltips at all. Another possibility, not so satisfactory, would be to have static annotations above the bars, with the corresponding counts…