[рони]

DarkPhoenix,

const double = x => x * 2;
function mapObject(fn, obj) {
  for (let i in obj) {
    if (obj.hasOwnProperty(i)) {
        obj[i] = double(obj[i]);
    }
  }
  return obj;
}
let obj = mapObject(double, {x: 1, y: 2, z: 3})
alert(JSON.stringify(obj, "", 4));