[danvk]

dygraphs has had that feature for about five years :)

There's also a "range selector" mode if you prefer the two-pane zooming interface: http://dygraphs.com/tests/range-selector.html

[BIackSwan]

I don't see the small window which shows the x & y co ordinates of the point you are hovering at. Is it it turned off by default?

[danvk]

Nope, it's in the top right of the chart. It shows values when you hover over the chart.