Object.assign, mergeObjectsShallow, mergeObjectsDeep

implementation.js

/**
 * Shallow merge objects
 */
function mergeObjectsShallow(target, ...sources) {
  for (let i = 0; i < sources.length; i++) {
    const source = sources[i];
    for (var prop in source) {
      if (!source.hasOwnProperty(prop)) continue;
      target[prop] = source[prop];
    }
  }
  return target;
}

/**
 * Deep merge objects
 */
function mergeObjectsDeep(target, ...sources) {
  for (let i = 0; i < sources.length; i++) {
    const source = sources[i];
    for (const prop in source) {
      if (!source.hasOwnProperty(prop)) continue;
      if (source[prop].constructor === Object) {
        target[prop] = mergeObjectsDeep({}, target[prop], source[prop]);
      } else {
        target[prop] = source[prop];
      }
    }
  }
  return target;
}

usage.js

/**
 * Object.assign() example
 */
var obj0_a = { aap: 1, noot: 2, mies: 3, wim: { wim1: 100, wim2: 200 } };
var obj0_b = { aap: 10, wim: { wim3: 300 } };
console.log(Object.assign({}, obj0_a, obj0_b));
//=> { aap: 10, noot: 2, mies: 3, wim: { wim3: 300 } }

/**
 * Shallow merge example
 */
var obj1_a = { aap: 1, noot: 2, mies: 3, wim: { wim1: 100, wim2: 200 } };
var obj1_b = { aap: 10, wim: { wim3: 300 } };
console.log(mergeObjectsShallow({}, obj1_a, obj1_b));
//=> { aap: 10, noot: 2, mies: 3, wim: { wim3: 300 } }

/**
 * Deep merge example
 */
var obj2_a = { aap: 1, noot: 2, mies: 3, wim: { wim1: 100, wim2: 200 } };
var obj2_b = { aap: 10, wim: { wim3: 300 } };
console.log(mergeObjectsDeep({}, obj2_a, obj2_b));
//=> { aap: 10, noot: 2, mies: 3, wim: { wim1: 100, wim2: 200, wim3: 300 } }