ways to merge objects (javascript)

object.merge.js

'use strict';

function merge_arguments() {
  let obj = {},
    i = 0,
    len = arguments.length,
    key;
  for (; i < len; i++) {
    for (key in arguments[i]) {
      if (arguments[i].hasOwnProperty(key)) {
        obj[key] = arguments[i][key];
      }
    }
  }
  return obj;
};

function merge_recursive(first, second) {
  for (let n in second) {
    if (typeof first[n] != 'object') {
      first[n] = second[n];
    } else if (typeof second[n] == 'object') {
      first[n] = merge_recursive(first[n], second[n]);
    }
  };
  return first;
};

const data_null = {
  null_key: 'null',
};
const data_first = {
  first_key: 'foo',
  tree_key: {
    one: 1,
    three: 3,
  }
};
const data_second = {
  second_key: 'bar',
  tree_key: {
    one: 0,
    two: 2,
  }
};

const res_spread = {...data_first, ...data_second};
const res_assign = Object.assign({}, data_first, data_second);

const res_jquery = $.extend({}, data_first, data_second);
const res_json = JSON.parse((JSON.stringify(data_first) + JSON.stringify(data_second)).replace(/\}\{/, ', '));

const res_arguments = merge_arguments({}, data_null, data_first, data_second);
const res_recursive = merge_recursive(data_first, data_second);

console.log('spread:');
console.log(res_spread);
console.log('assign:');
console.log(res_assign);

console.log('jquery:');
console.log(res_jquery);
console.log('JSON:');
console.log(res_json);

console.log('merge_arguments:');
console.log(res_arguments);
console.log('merge_recursive:');
console.log(res_recursive);