Like Object.assign. But deep.

deepAssign.js

const deepAssign = (target, ...sources) =>
    sources.reduce((total, src) =>
        Object.keys(src).reduce((agg, n) =>
            Object.assign({}, agg, {
                [n]: (
                    typeof src[n] === "object" ?
                    deepAssign(target[n] || {}, src[n]) :
                    src[n]
                )
            }),
            total),
        target)