Redux reduceReducers in ES5

reduceReducers.js

var reduceReducers = function () {
    var reducers = [].slice.call(arguments);

    return function (previous, current) {
        return reducers.reduce(function (accu, curr) {
            return curr(accu, current);
        }, previous);
    };
};

reduceReducers.test.js

var reduceReducers = require('./reduceReducers');

describe('reduceReducers', function () {
    it('combines multiple reducers into a single reducer', function () {
        var reducerA = function (prev, curr) {
            return Object.assign({}, prev, { A: prev.A + curr });
        };
        var reducerB = function (prev, curr) {
            return Object.assign({}, prev, { B: prev.B * curr });
        };
        var reducer = reduceReducers(reducerA, reducerB);

        expect(reducer({ A: 1, B: 2 }, 3)).to.deep.equal({ A: 4, B: 6 });
        expect(reducer({ A: 5, B: 8 }, 13)).to.deep.equal({ A: 18, B: 104 });
    });

    it('chains multiple reducers into a single reducer', function () {
        var addReducer = function (prev, curr) {
            return Object.assign({}, prev, { A: prev.A + curr });
        };
        var multReducer = function (prev, curr) {
            return Object.assign({}, prev, { A: prev.A * curr });
        };
        var reducerAddMult = reduceReducers(addReducer, multReducer);
        var reducerMultAdd = reduceReducers(multReducer, addReducer);

        expect(reducerAddMult({ A: 1, B: 2 }, 3)).to.deep.equal({ A: 12, B: 2 });
        expect(reducerMultAdd({ A: 1, B: 2 }, 3)).to.deep.equal({ A: 6, B: 2 });
    });
});