redux-structure-flow.js

// actions.js
// @flow
export type SetHeightAction = {
    type: 'box/SET_COLOR',
    height: number
};

export type SetColor = {
    type: 'box/SET_COLOR',
    color: string
};

export type Action =
    | SetHeightAction
    | SetWidthAction;

export function setDimensions(height: number, width: number): SetHeightAction {
    return {
        type: 'box/SET_DIMENSIONS',
        height,
        width
    };
}

export function setWidth(color: string): SetColor {
    return {
        type: 'box/SET_COLOR',
        color
    };
}

// reducers.js
// @flow
import {initialState} from './data';
import type {State} from './data';
import type {Action} from './actions';

export default function box(state: State = initialState, action: Action): State {
    switch (action.type) {
        case 'box/SET_DIMENSIONS':
            return setDimensions(state, action);
        case 'box/SET_COLOR':
            return setColor(state, action);
        default:
            return state;
    }
}

function setDimensions(state, action) {
    return {
        ...state,
        height: action.height,
        width: action.width
    };
}

function setColor(state, action) {
    return {
        ...state,
        color: action.color
    };
}