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How to join two JavaScript Objects, without using JQUERY

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There are couple of different solutions to achieve this:
1 - Native javascript for-in loop:
const result = {};
let key;

for (key in obj1) {
  if(obj1.hasOwnProperty(key)){
    result[key] = obj1[key];
  }
}

for (key in obj2) {
  if(obj2.hasOwnProperty(key)){
    result[key] = obj2[key];
  }
}
const result = {};

Object.keys(obj1)
  .forEach(key => result[key] = obj1[key]);

Object.keys(obj2)
  .forEach(key => result[key] = obj2[key]);
3 - Object.assign():
(Browser compatibility: Chrome: 45, Firefox (Gecko): 34, Internet Explorer: No support, Edge: (Yes), Opera: 32, Safari: 9)
const result = Object.assign({}, obj1, obj2);
Defined in several sections of the specification: Array InitializerArgument Lists
Using this new syntax you could join/merge different objects into one object like this:
const result = {
  ...obj1,
  ...obj2,
};
Merge the contents of two or more objects together into the first object.
const target = {};

$.extend(target, obj1, obj2);
Run a deep merge of the contents of two or more objects together into the target. Passing false for the first argument is not supported.
const target = {};

$.extend(true, target, obj1, obj2);
7 - Lodash _.assignIn(object, [sources]): also named as _.extend:
const result = {};

_.assignIn(result, obj1, obj2);
const result = _.merge(obj1, obj2);
There are a couple of important differences between lodash's merge function and Object.assign:
1- Although they both receive any number of objects but lodash's merge apply a deep merge of those objects but Object.assign only merges the first level. For instance:
_.isEqual(_.merge({
  x: {
    y: { key1: 'value1' },
  },
}, {
  x: {
    y: { key2: 'value2' },
  },
}), {
  x: {
    y: {
      key1: 'value1',
      key2: 'value2',
    },
  },
}); // true
BUT:
const result = Object.assign({
  x: {
    y: { key1: 'value1' },
  },
}, {
  x: {
    y: { key2: 'value2' },
  },
});
_.isEqual(result, {
  x: {
    y: {
      key1: 'value1',
      key2: 'value2',
    },
  },
}); // false
// AND
_.isEqual(result, {
  x: {
    y: {
      key2: 'value2',
    },
  },
}); // true
2- Another difference has to do with how Object.assign and _.merge interpret the undefinedvalue:
_.isEqual(_.merge({x: 1}, {x: undefined}), { x: 1 }) // false
BUT:
_.isEqual(Object.assign({x: 1}, {x: undefined}), { x: undefined })// true

Update 1:
When using for in loop in JavaScript, we should be aware of our environment specially the possible prototype changes in the JavaScript types. For instance some of the older JavaScript libraries add new stuff to Array.prototype or even Object.prototype. To safeguard your iterations over from the added stuff we could use object.hasOwnProperty(key) to mke sure the key is actually part of the object you are iterating over.

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