* Move all helpers into src/helpers
* Move curve helpers to their own file
* DOM helpers moved to their own file
* Update migration docs
* Remove migration docs on new functions
In order to be compatible with any CSP, we need to prevent the automatic creation of the DOM 'style' element and offer our CSS as a separate file that can be manually loaded (`Chart.js` or `Chart.min.js`). Users can now opt-out the style injection using `Chart.platform.disableCSSInjection = true` (note that the style sheet is now injected on the first chart creation).
To prevent duplicating and maintaining the same CSS code at different places, move all these rules in `platform.dom.css` and write a minimal rollup plugin to inject that style as string in `platform.dom.js`. Additionally, this plugin extract the imported style in `./dist/Chart.js` and `./dist/Chart.min.js`.
If the container size shrank during chart resize, let's assume scrollbar appeared. So we resize again with the scrollbar visible effectively making chart smaller and the scrollbar hidden again. Because we are inside `throttled`, and currently `ticking`, scroll events are ignored during this whole 2 resize process. If we assumed wrong and something else happened, we are resizing twice in a frame (potential performance issue)
Chrome specific issue that happens when destroying a chart and re-creating it immediately (same animation frame?). The CSS animation used to detect when the canvas become visible is not re-evaluated, breaking responsiveness. Accessing the `offsetParent` property will force a reflow and re-evaluate the CSS animation.
If `window` or `document` are `undefined`, a minimal platform implementation is used instead, which one only returns a context2d read from the given canvas/context.
Allow to create a chart on a canvas not yet attached to the DOM (detection based on CSS animations described in https://davidwalsh.name/detect-node-insertion). The resize element (IFRAME) is added only when the canvas receives a parent or when `style.display` changes from `none`. This change also allows to re-parent the canvas under a different node (the resizer element following). This is a preliminary work for the DIV based resizer.
Properly export helpers and remove dependencies to `Chart.helpers`. Helpers can now be accessed from `src/helpers/index.js` (`var helpers = require('path/to/helpers/index')`, instead of `var helpers = Chart.helpers`).
Deprecate `addEvent` and `removeEvent`, and move implementation in `platform.dom.js`. Add 'options' feature detection to register event listeners as passive and prevent warning in Chrome.
Move some of the "core" and "canvas" utils in `helpers.core.js` and `helpers.canvas.js` and introduce the new `isNullOrUndef` and `isObject` helpers. Deprecate `indexOf` and rename `drawRoundedRectangle` to `roundedRect` which now creates a simple `rect` path if radius is 0. Write missing unit tests for the moved helpers.
`instanceof HTMLCanvasElement/CanvasRenderingContext2D` fails when the item is inside an iframe or when running in a protected environment. We could guess the types from their toString() value but let's keep things flexible and assume it's a sufficient condition if the item has a context2D which has item as `canvas`.
Move base platform definition and logic in src/platform/platform.js and simplify the browser -> Chart.js event mapping by listing only different naming then fallback to the native type.
Replace `createEvent` by `add/removeEventListener` methods which dispatch Chart.js IEvent objects instead of native events. Move `add/removeResizeListener` implementation into the DOM platform which is now accessible via `platform.add/removeEventListener(chart, 'resize', listener)`.
Finally, remove `bindEvent` and `unbindEvent` from the helpers since the implementation is specific to the chart controller (and should be private).
Refactoring to put browser specific code in a new class, BrowserPlatform.
BrowserPlatform implements IPlatform. Chart.Platform is the constructor for the platform object that is attached to the chart instance.
Plugins are notified about the event using the `onEvent` call. The legend plugin was converted to use onEvent instead of the older private `handleEvent` method.
Wrote test to check that plugins are notified about events
