updux/src/actions.js

export function isActionGen(action) {
    return typeof action === 'function' && action.type;
}

export function action(type, payloadFunction, transformer) {
    let generator = function (...payloadArg) {
        const result = { type };

        if (payloadFunction) {
            result.payload = payloadFunction(...payloadArg);
        } else {
            if (payloadArg[0] !== undefined) result.payload = payloadArg[0];
        }

        return result;
    };

    if (transformer) {
        const orig = generator;
        generator = (...args) => transformer(orig(...args), args);
    }

    generator.type = type;

    return generator;
}