Use const / let for variable declarations

[benmccann]

When we release the next major version, we should at least use const, which is supported natively in all browsers we support

let is supported in all browsers except Opera Mini. We would need to decide if we want to support Opera Mini or not

[jledentu]

Did you consider using Babel to allow the use of let (and other ES2015+ syntax) in the code and transpile it automatically into compatible code for all supported browsers?

[simonbrunel]

@jledentu we don't want to introduce Babel in v2, that's why we are considering that move only in v3.

But IMO, even in v3, we should still transpile both to var to target more platforms, not only browsers.

[sebiniemann]

With using Babel in v3 to transpile the source, many more recent language features could be used, like rewriting

Chart.js/src/core/core.controller.js

Lines 188 to 195 in e6d5896

	Object.defineProperty(me, 'data', {
	get: function() {
	return me.config.data;
	},
	set: function(value) {
	me.config.data = value;
	}
	});

to (and moving it outside the constructor)

get data() {
  return this.config.data;
},
set data(value) {
  this.config.data = value;
}

However, this could also be done step by step as long as the original, non-transpiled source is handled like a private code base after this. I believe this would ease the development a lot, as new language features could be added step by step, instead of introducing a breaking change every time.

[benmccann]

This is largely done in the main codebase. Not yet in the tests