title: Bokeh: CustomJS Callback for Mouse Move or Click
body: <p>I want to update my plot data based on the current mouse position.</p>
  
  <p>What I'm aiming for is something like the <a href="http://bokeh.pydata.org/en/0.10.0/docs/user_guide/interaction.html#customjs-for-widgets" rel="nofollow">interactive power function plot</a>, but instead of taking the exponent from a slider, take the exponent to be the current x-value of the mouse cursor (in plot coordinate space, not display coordinates).</p>
  
  <p>If it's not possible to get an onMouseMove callback, onClick would also be ok. However, I don't want to have to click a specific graph (then I could use TapTool), but tapping anywhere in the plot should suffice.</p>