When you reduce a function from 16 lines to this, you know ES6 is in good hands now.

You can do
const { years, period_types } = this

Shortening by one more line😃

@leksyib that's cool, i always love to learn such shortcuts

The sick thing about this is, imo it even improves readability.

In perl for example such one-liners get plain black magic pretty fast but in js, with implicit returns, object deconstruction and stuff you understand it even better.

I would avoid side-effects by making years and period_types and all_periods arguments of this function. Makes unit-testing much easier as you are not dependent on an object state.

Aim for pure functions.

@k0pernikus probably a class method

And they say they hate js... ^_^

@k0pernikus nice, though it's Vue so it's easier that way