Fixes #4772: added scope for tooltip position mode call and added docs

[fsmeier]

See linked issue for more information #4772

[fsmeier]

@etimberg Is this ok? I think the biggest change here is the extended entry in the documentation :D

[simonbrunel]

Looks good, could be great to also include a unit test that checks expected arguments / scope.

[fsmeier]

@simonbrunel
Actually I tried to run gulp unittest, but it seems not to work inside my current setup docker-container. Any suggested container for this project?

22 09 2017 08:42:30.496:INFO [framework.browserify]: bundle built
22 09 2017 08:42:30.516:INFO [karma]: Karma v1.7.1 server started at http://0.0.0.0:9876/
22 09 2017 08:42:30.516:INFO [launcher]: Launching browsers Firefox, Chrome with unlimited concurrency
22 09 2017 08:42:30.526:INFO [launcher]: Starting browser Firefox
22 09 2017 08:42:30.536:INFO [launcher]: Starting browser Chrome
22 09 2017 08:42:30.536:ERROR [launcher]: No binary for Chrome browser on your platform.

[benmccann]

I just did a quick google. It seems like the one below has node, chrome, and firefox. I haven't tested to see if it works with chart.js or not
https://hub.docker.com/r/atlassianlabs/docker-node-jdk-chrome-firefox/~/dockerfile/

[etimberg]

Agree about the unit test. Once we that's in this is good to merge IMO

[fsmeier]

Yes! It is still on my todo. Planed it for tomorrow. The last two weeks were a bit stressful at work ;)

[benmccann]

Thanks for adding the unit test!

[simonbrunel]

It doesn't work because if the method is not called, then expectations are not evaluated. We could use spyOn instead to be sure that the method is actually called, something like that:

var scope = null;

Chart.Tooltip.positioners.test = function() {
    scope = this;
    return {x: 0, y: 0};
};

spyOn(Chart.Tooltip.positioners, 'test');

// {...}

node.dispatchEvent(evt);

var fn = Chart.Tooltip.positioners.test;
expect(fn.calls.count()).toBe(1);
expect(fn.calls.first().args[0] instanceof Array).toBe(true);
expect(fn.calls.first().args[1].hasOwnProperty('x')).toBe(true);
expect(fn.calls.first().args[1].hasOwnProperty('y')).toBe(true);
expect(scope instanceof Chart.Tooltip).toBe(true);

[fsmeier]

@simonbrunel I resolved your requested changes. Was a bit tricky...

[simonbrunel]

@IMM0rtalis LGTM, thanks!

expect(fn.calls.first().object instanceof Chart.Tooltip).toBe(true);

I knew about this object property on the call object but I thought it was referring to the spied object (Chart.Tooltip.positioners), not thisArg. Nice!

[fsmeier]

Actually I had to look for alternatives to scope = this. Scope was undefined all the time so I was wondering if the spyOn is not storing the context somehow.