title: How to define x-axis hover format when using plotly.js
body: <p>In examples such as this one: <a href="https://plot.ly/12/~streaming-demos/" rel="nofollow">https://plot.ly/12/~streaming-demos/</a>, by using the designer tools under axes > Labels > Hover Format I am able to change the format of the time x-axis tooltip to something like "%y/%m/%d %I:%M%p"). How do I achieve the same thing in code?</p>
  
  <p>I have been through the reference (<a href="https://plot.ly/javascript/reference/" rel="nofollow">https://plot.ly/javascript/reference/</a>) and can't find anything on this.</p>