Tooltip extensions (onShown,onHidden, linked) and reference to all chart instances

[rshingleton]

Ref #308

Adding reference to bb.instances: Chart.internals.charts
see: src/core.js

bb already had a feature that stored all chart instances. This PR adds a reference to this collection in the Chart.internals that can be used elsewhere (see linked tooltip option)

Adding tooltip options: onShown: function, onHidden: function tooltip

tooltip: {
   onShown: function(){
    	// 'this' will give a reference to data from tooltip.js showTooltip method.
    	// data	available:
    	// chart: reference to the chart instance
    	// element: html element
    	// height
    	// width
    	// selectedData: data associated with tooltip {x: Tue Jan 01 2013 00:00:00 GMT-0500 (EST), value: 10, id: "data", index: 0, name: "data"}
    	// x: x coordinate from the first data element
    	// position: {top: 0, left: 0}
   	  console.log(this);
   },
   onHidden: function(){
   	  // 'this' will give a reference to chart
   	  console.log(this);
   },
}

Adding tooltip option: linked: boolean

tooltip: {
   // Link any tooltips when multiple charts are on the screen
   linked: true // default false
}

Makes use of Chart.internals.charts which has a reference to bb.instances. Any charts in the bb.instances that are currently rendered will show tooltips at like x axis.

Basic demo file at: /demo/linked-tooltips.html

[rshingleton]

Not sure how to add more than one chart to a single demo page in the demo.js, I'll look into it more unless someone can point me in the right direction.

[rshingleton]

I updated the demo area, chart.js to allow multiple charts in a demo by checking for an array of options and handling them during chart generation.

• Updated chart.js to check for array type options and render multiple charts
• Added Alertify.js to the demo to demonstrate callback functions
• Added additional validation in the linked tooltip logic to validate that charts in the bb.instance array are actually in the DOM. Ran into an issue in the demo area where chart instances had been removed from the DOM but were still referenced in the bb.instance array, causing an exception. May need to put some validation in core.js to check for valid chart instances

[netil]

It looks a nice idea! It can create multiple charts with tooltip linked.

Aside of the review comments, it needs to have:

• API jsdoc for the documentation
• Test codes

[netil]

Most of this block is duplicated on hide also.
It should making as a separated function to handle both states (showing & hiding).

[rshingleton]

Moving this to a separate handler function.

[netil]

There're already undocumented tooltip.onshow/onhide options.
It'll be good using them instead.

[rshingleton]

I saw these, but they don't functioning in (what I consider) the expected manner. The current implementation is called in the show() method of api.tooltip.js. It fires once when the tooltip is originally shown and then never again. If the tooltips are linked, they will fire all the time because the show method is called explicitly in the linked tooltip handler.

I'll look at the implementation some more today.

[netil]

Using ES6 syntax is good, but as having IE9 support this won't work for old browsers.
This is the reason of keeping old syntax.

[rshingleton]

Roger that. Converting back to var notation.

[rshingleton]

I'll work on some tests this weekend.

[rshingleton]

Adding tests in tooltip-spec.js
Tooltip callbacks tests:

• Check tooltip callbacks are executed and in proper order

Linked Tooltips tests:

• Check positions and data ordering on associated charts when one chart tooltip event is executed

[netil]

Thanks @rshingleton! I just merged with some changes.
It'll be more easier to interchange ideas if the changed range is more smaller than this one.

Anyway, really appreciate again your efforts on this!