pick and reject

pick-reject.js

function reject(obj, keys) {
    return Object.keys(obj)
        .filter(k => !keys.includes(k))
        .map(k => Object.assign({}, {[k]: obj[k]}))
        .reduce((res, o) => Object.assign(res, o), {});
}

function pick(obj, keys) {
    return keys.map(k => k in obj ? {[k]: obj[k]} : {})
               .reduce((res, o) => Object.assign(res, o), {});
}