Reorganize internal dependencies

[simonbrunel]

The actual code base doesn't import features but fully relies on Chart.* (e.g. Chart.helpers, Chart.defaults, etc...). Files are imported in chart.js in the order they are supposed to depend from each other. As far as I tried, this makes very complicated to safely and properly import a subset of the library.

We could reorganize the library to use require('path/to/features') instead of Chart.{feature} and so remove all function export and Chart.* references.

var helpers = require('../helpers');    // instead of = Chart.helpers
var defaults = require('../defaults');  // instead of = Chart.defaults
//...

The Chart namespace would be fully populated in chart.js:

// chart.js
var Chart = require('./core/core.controller');
Chart.defaults = require('./core/core.defaults');
Chart.helpers = require('./helpers/index');
Chart.controllers = require('./controllers/index');
// ...

Removing the "function export" impacts a lot of lines (remove one tab almost everywhere), so we could do that step by step to avoid huge and painful reviews and limit conflicts with open PRs. I would sequentially split the work as follows:

• Make Chart.helpers importable #4479 export Chart.helpers.*, import src/helpers/index
• Make Chart.defaults/Ticks/Interaction importable #4512 export Chart.defaults.*, import src/core/core.defaults
• Make Chart.plugins importable #5114, Make Chart.Animation/animations/Tooltip importable #5382, Make the main controller importable #5969 export Chart.* from core classes
• Make Chart.Element/elements.* importable #4540 export Chart.elements.*, import src/elements/index
• Make Chart.controllers.* importable #5871 export Chart.controllers.*, import src/controllers/index
• Cleanup scales export for better import strategy #5953 export Chart.scales.*, import src/scales/index
• Make Chart.platform importable #4509 export Chart.platform.*, import src/platform/platform
• Make Chart.plugins importable #5114 export Chart.plugins.*, import src/plugins/index
• Deprecate Chart.{Type} classes #5868 deprecate Chart.* (from `src/charts/*.js)

This is a preliminary work in order to migrate to ES6 modules (discussed in #2466, #4461, #4303, etc.). Awesome work as been done by @salzhrani but I believe that trying to do everything in one step (including ES6 new features) will take time, be hard or even impossible to review / handle conflicts with incoming contributions and finally takes forever to land in master.

Thoughts?

[salzhrani]

This is super awesome.
I would also suggest switching to rollup once all is done.

[simonbrunel]

It's planned :)

[pndewit]

Any progress on this? I'd love to see this one added to the 2.8 milestones! 👍

[etimberg]

@pndewit would be a nice feature, unfortunately both @simonbrunel and I are crazy busy right now so we aren't able to do it ourselves.

[yahya-uddin]

Any progress on this?

[benmccann]

The code uses import everywhere now, so I'm going to consider this done. #6935