Detailed explanation of specific usage code examples of how to merge objects in Node.js

In Node.js, we can merge two objects through underscore's extend or lodash's merge, but how to deal with complex objects like the following?

Node.js merges two complex objects

For example, there are the following two objects:

var obj1 = {
 "name" : "myname",
 "status" : 0,
 "profile": { "sex":"m", "isactive" : true},
 "strarr":["one", "three"],
 "objarray": [
 {
  "id": 1,
  "email": "a1@me.com",
  "isactive":true
 },
 {
  "id": 2,
  "email": "a2@me.com",
  "isactive":false
 }
 ]
};

var obj2 = {
 "name" : "myname",
 "status" : 1,
 "newfield": 1,
 "profile": { "isactive" : false, "city": "new York"},
 "strarr":["two"],
 "objarray": [
 {
  "id": 1,
  "isactive":false
 },
 {
  "id": 2,
  "email": "a2modified@me.com"
 },
 {
  "id": 3,
  "email": "a3new@me.com",
  "isactive" : true
 }
 ]
};

I hope that the result after the merger will be output as follows:

{ name: 'myname',
 status: 1,
 profile: { sex: 'm', isactive: false, city: 'new York' },
 strarr: [ 'one', 'three', 'two' ],
 objarray: 
 [ { id: 1, email: 'a1@me.com', isactive: false },
 { id: 2, email: 'a2modified@me.com', isactive: false },
 { id: 3, email: 'a3new@me.com', isactive: true } ],
newfield: 1 }

We cannot achieve the above results through the existing methods of underscore or lodash, so we can only write it ourselves. The code is implemented.

function mergeObjs(def, obj) {
 if (!obj) {
 return def;
 } else if (!def) {
 return obj;
 }

 for (var i in obj) {
 // if its an object
 if (obj[i] != null && obj[i].constructor == Object)
 {
  def[i] = mergeObjs(def[i], obj[i]);
 }
 // if its an array, simple values need to be joined. Object values need to be remerged.
 else if(obj[i] != null && (obj[i] instanceof Array) && obj[i].length > 0)
 {
  // test to see if the first element is an object or not so we know the type of array we're dealing with.
  if(obj[i][0].constructor == Object)
  {
  var newobjs = [];
  // create an index of all the existing object IDs for quick access. There is no way to know how many items will be in the arrays.
  var objids = {}
  for(var x= 0, l= def[i].length ; x < l; x++ )
  {
   objids[def[i][x].id] = x;
  }

  // now walk through the objects in the new array
  // if the ID exists, then merge the objects.
  // if the ID does not exist, push to the end of the def array
  for(var x= 0, l= obj[i].length; x < l; x++)
  {
   var newobj = obj[i][x];
   if(objids[newobj.id] !== undefined)
   {
   def[i][x] = mergeObjs(def[i][x],newobj);
   }
   else {
   newobjs.push(newobj);
   }
  }

  for(var x= 0, l = newobjs.length; x<l; x++) {
   def[i].push(newobjs[x]);
  }
  }
  else {
  for(var x=0; x < obj[i].length; x++)
  {
   var idxObj = obj[i][x];
   if(def[i].indexOf(idxObj) === -1) {
    def[i].push(idxObj);
   }
  }
  }
 }
 else
 {
  def[i] = obj[i];
 }
 }
 return def;}

By slightly improving the above code, we can automatically add Number type values ​​during the merging process.

function merge(def, obj) {
 if (!obj) {
  return def;
 }
 else if (!def) {
  return obj;
 }

 for (var i in obj) {
  // if its an object
  if (obj[i] != null && obj[i].constructor == Object)
  {
   def[i] = merge(def[i], obj[i]);
  }
  // if its an array, simple values need to be joined. Object values need to be re-merged.
  else if(obj[i] != null && (obj[i] instanceof Array) && obj[i].length > 0)
  {
   // test to see if the first element is an object or not so we know the type of array we're dealing with.
   if(obj[i][0].constructor == Object)
   {
    var newobjs = [];
    // create an index of all the existing object IDs for quick access. There is no way to know how many items will be in the arrays.
    var objids = {}
    for(var x= 0, l= def[i].length ; x < l; x++ )
    {
     objids[def[i][x].id] = x;
    }

    // now walk through the objects in the new array
    // if the ID exists, then merge the objects.
    // if the ID does not exist, push to the end of the def array
    for(var x= 0, l= obj[i].length; x < l; x++)
    {
     var newobj = obj[i][x];
     if(objids[newobj.id] !== undefined)
     {
      def[i][x] = merge(def[i][x],newobj);
     }
     else {
      newobjs.push(newobj);
     }
    }

    for(var x= 0, l = newobjs.length; x<l; x++) {
     def[i].push(newobjs[x]);
    }
   }
   else {
    for(var x=0; x < obj[i].length; x++)
    {
     var idxObj = obj[i][x];
     if(def[i].indexOf(idxObj) === -1) {
      def[i].push(idxObj);
     }
    }
   }
  }
  else
  {
   if (isNaN(obj[i]) || i.indexOf(&#39;_key&#39;) > -1){
    def[i] = obj[i];
   }
   else{
    def[i] += obj[i];
   }
  }
 }
 return def;
}

For example, there are the following two objects:

var data1 = {
 "_id" : "577327c544bd90be508b46cc",
 "channelId_info" : [
 {
  "channelId_key" : "0",
  "secondLevel_group" : [
  {
   "secondLevel_key" : "568cc36c44bd90625a045c60",
   "sender_group" : [
   {
    "sender_key" : "577327c544bd90be508b46cd",
    "sender_sum" : 40.0
   }
   ],
   "senders_sum" : 40.0
  }
  ],
  "channelId_sum" : 40.0
 }
 ],
 "car_sum" : 40.0
};

var data2 = {
 "_id" : "577327c544bd90be508b46cc",
 "channelId_info" : [
 {
  "channelId_key" : "0",
  "secondLevel_group" : [
  {
   "secondLevel_key" : "568cc36c44bd90625a045c60",
   "sender_group" : [
   {
    "sender_key" : "577327c544bd90be508b46cd",
    "sender_sum" : 20.0
   },
   {
    "sender_key" : "5710bcc7e66620fd4bc0914f",
    "sender_sum" : 5.0
   }
   ],
   "senders_sum" : 25.0
  },
  {
   "secondLevel_key" : "55fbeb4744bd9090708b4567",
   "sender_group" : [
   {
    "sender_key" : "5670f993a2f5dbf12e73b763",
    "sender_sum" : 10.0
   }
   ],
   "senders_sum" : 10.0
  }
  ],
  "channelId_sum" : 35.0
 },
 {
  "channelId_key" : "1",
  "secondLevel_group" : [
  {
   "secondLevel_key" : "568cc36c44bd90625a045c60",
   "sender_group" : [
   {
    "sender_key" : "577327c544bd90be508b46cd",
    "sender_sum" : 20.0
   }
   ],
   "senders_sum" : 20.0
  }
  ],
  "channelId_sum" : 20.0
 }
 ],
 "car_sum" : 55.0
};

The result after merging is as follows:

{
 "_id": "577327c544bd90be508b46cc",
 "channelId_info": [
  {
   "channelId_key": "0",
   "secondLevel_group": [
    {
     "secondLevel_key": "568cc36c44bd90625a045c60",
     "sender_group": [
      {
       "sender_key": "577327c544bd90be508b46cd",
       "sender_sum": 60
      },
      {
       "sender_key": "5710bcc7e66620fd4bc0914f",
       "sender_sum": 5
      }
     ],
     "senders_sum": 65
    },
    {
     "secondLevel_key": "55fbeb4744bd9090708b4567",
     "sender_group": [
      {
       "sender_key": "5670f993a2f5dbf12e73b763",
       "sender_sum": 10
      }
     ],
     "senders_sum": 10
    }
   ],
   "channelId_sum": 75
  },
  {
   "channelId_key": "1",
   "secondLevel_group": [
    {
     "secondLevel_key": "568cc36c44bd90625a045c60",
     "sender_group": [
      {
       "sender_key": "577327c544bd90be508b46cd",
       "sender_sum": 20
      }
     ],
     "senders_sum": 20
    }
   ],
   "channelId_sum": 20
  }
 ],
 "car_sum": 95
}

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