What replaces y-axis with v 2.4 mode upgrades?

[arxpoetica]

With the mode and intersect changes in v. 2.4.0, it's not clear what to replace y-axis with. (See #3400 for history on this.)

Steps to Reproduce

See: https://jsbin.com/bevabi/4/edit?html,css,js,output

1. Hover above the bars on the (vertical) bar chart.

2. Note that with mode: 'index' and intersect: false set, the whole region highlights both sets of data.
   

3. Now hover to the right of the horizontal bars not on the bar themselves. Note that they do not get updated, unlike the vertical bar chart.
   

Context

In the past, I just used x-axis and y-axis. With index replacing x-axis, what replaces y-axis now?

Environment

• Chart.js version: 2.5.0
• Browser name and version: Google Chrome Version 56.0.2924.87 (64-bit)
• Link to your project: https://jsbin.com/bevabi/4/edit?html,css,js,output

[etimberg]

We should provide a similar mode but that works in the Y direction, perhaps 'index-y'. I tried the y mode but it didn't have good results.

As a work around, you could define your own mode by adding a handler to the Chart.Interaction.modes map. https://github.com/chartjs/Chart.js/blob/master/src/core/core.interaction.js