add support for typed arrays

[kurkle]

https://codepen.io/kurkle/pen/jXEwYe

Fixes #4920

[simonbrunel]

Thanks @kurkle.

helpers.isArray is used a lot even outside this project, so we need to be sure that returning true for all arrays (basic and typed) will not break existing code. Is there any use case where we don't want to handle both the same way?

[kurkle]

There is one place, where I get the idea this could break outside code
(in src/core/core.tooltip.js):

// Helper to push or concat based on if the 2nd parameter is an array or not
function pushOrConcat(base, toPush) {
	if (toPush) {
		if (helpers.isArray(toPush)) {
			// base = base.concat(toPush);
			Array.prototype.push.apply(base, toPush);
		} else {
			base.push(toPush);
		}
	}

	return base;
}

Here, if base would be typed array, Array.prototype.push.apply would not work. This is never the case inside this lib though (and base is not actually tested with isArray anyway).

So if someone tested with helpers.isArray and based on that tried to push, it would break. There's no push/pop in typed arrays.

[simonbrunel]

I didn't know that typed arrays didn't support push/pop. I don't think that's an issue because it would fail only if this library or external plugins try to alter the size of a typed array after checking helpers.isArray(). In that case, the code expects a resizeable array, meaning that it's either an internal bug (use of the wrong structure) or a bad user input.

If that's the only difference, I think it's safe to merge (though, not fully confident).

@etimberg @nagix do you think of use cases that this PR would break?

[simonbrunel]

Thanks @kurkle

[simonbrunel]

It should be fine if our tests use es6 features, we only don't want our sources to use es6 feature because we don't want to integrate babel in v2.