FluxStateIterator.js

const INCREMENT = 'INCREMENT', DECREMENT = 'DECREMENT';

function reducer(state, action) {
	switch (action.type) {
	case INCREMENT:
		return state + 1;
	case DECREMENT:
		return state - 1;
	}
}

function* states(reducer, initialState) {
	while (true) {
		// yield returns an argument that was passed in .next()
		initialState = reducer(initialState, yield initialState);
	}
}

var appState = states(reducer, 0);

// first .next() call ignores passed arguments 
// (or I didn't use generator correctly)
console.log(appState.next());

// each time iterator will update the state with provided action and return new state
console.log(appState.next({ type: INCREMENT }));
console.log(appState.next({ type: INCREMENT }));
console.log(appState.next({ type: INCREMENT }));
console.log(appState.next({ type: DECREMENT }));

I tried to find a bit of info about the issue commented in line 21 - 22 but came up empty handed. I haven't used generators myself yet and am unaware what the right thing to do is. Thanks again for the English comments, they helped a lot. Very interesting and clean idea!

21 - 22 is fine, that's the way generators are meant to work, it will run the generator to the first yield and then pause it. Next time you call next it picks up from there hence a passed in argument now being used.