deep merge objects with AngularJS

Normally to shallow copy objects I would use angular.extend()

Here's an example of that:

var object1 = {
  "key": "abc123def456",
  "message": {
    "subject": "Has a Question",
    "from": "[email protected]",
    "to": "[email protected]"
   }
};

var object2 = {
  "key": "00700916391"
};

console.log(angular.extend({}, object1, object2));

Would give us:

{
 "key": "00700916391",
 "message": {
   "subject": "Has a Question",
   "from": "[email protected]",
   "to": "[email protected]"
  }
}

But what if I wanted to merge objects so that parent keys are not over written by child objects:

var object1 = {
  "key": "abc123def456",
  "message": {
    "subject": "Has a Question",
    "from": "[email protected]",
    "to": "[email protected]"
   }
};

var object2 = {
  "key": "00700916391",              //Overwrite me
  "message": {                       //Dont overwrite me!
    "subject": "Hey what's up?",     //Overwrite me
    "something": "something new"     //Add me
   }
};

console.log(merge(object1, object2));

Would give us:

{
 "key": "00700916391",
 "message": {
   "subject": "Hey what's up?",
   "from": "[email protected]",
   "to": "[email protected]",
   "something": "something new"
  }
}

• Is there an Angular function that already does a deep merge that I am not aware of?

• If not is there a native way to do this in javascript recursively for n levels deep?

Solution 1:

Angular 1.4 or later

Use angular.merge:

Unlike extend(), merge() recursively descends into object properties of source objects, performing a deep copy.

angular.merge(object1, object2); // merge object 2 into object 1

Older versions of Angular:

There is no reason a simple recursive algorithm shouldn't work :)

Assuming they're both the result of JSON.stringify or similar:

function merge(obj1,obj2){ // Our merge function
    var result = {}; // return result
    for(var i in obj1){      // for every property in obj1 
        if((i in obj2) && (typeof obj1[i] === "object") && (i !== null)){
            result[i] = merge(obj1[i],obj2[i]); // if it's an object, merge   
        }else{
           result[i] = obj1[i]; // add it to result
        }
    }
    for(i in obj2){ // add the remaining properties from object 2
        if(i in result){ //conflict
            continue;
        }
        result[i] = obj2[i];
    }
    return result;
}

Here is a working fiddle

(Note, arrays are not handled here)

Solution 2:

In the new version of Angularjs they added merge function which will perform the deep copy.

For the older versions, I have created my custom function by copying the code of merge function from new version of Angularjs. Below is the code for the same,

function merge(dst){
  var slice = [].slice;
  var isArray = Array.isArray;
  function baseExtend(dst, objs, deep) {
    for (var i = 0, ii = objs.length; i < ii; ++i) {
      var obj = objs[i];
      if (!angular.isObject(obj) && !angular.isFunction(obj)) continue;
      var keys = Object.keys(obj);
      for (var j = 0, jj = keys.length; j < jj; j++) {
        var key = keys[j];
        var src = obj[key];
        if (deep && angular.isObject(src)) {
          if (!angular.isObject(dst[key])) dst[key] = isArray(src) ? [] : {};
          baseExtend(dst[key], [src], true);
        } else {
          dst[key] = src;
        }
      }
    }

    return dst;
  }
  return baseExtend(dst, slice.call(arguments, 1), true);
}

Hope this will help someone who is wondering why angular.merge is not working in older versions.

Solution 3:

angular.merge polyfill for angular < 1.4.0

if (!angular.merge) {
  angular.merge = (function mergePollyfill() {
    function setHashKey(obj, h) {
      if (h) {
        obj.$$hashKey = h;
      } else {
        delete obj.$$hashKey;
      }
    }

    function baseExtend(dst, objs, deep) {
      var h = dst.$$hashKey;

      for (var i = 0, ii = objs.length; i < ii; ++i) {
        var obj = objs[i];
        if (!angular.isObject(obj) && !angular.isFunction(obj)) continue;
        var keys = Object.keys(obj);
        for (var j = 0, jj = keys.length; j < jj; j++) {
          var key = keys[j];
          var src = obj[key];

          if (deep && angular.isObject(src)) {
            if (angular.isDate(src)) {
              dst[key] = new Date(src.valueOf());
            } else {
              if (!angular.isObject(dst[key])) dst[key] = angular.isArray(src) ? [] : {};
              baseExtend(dst[key], [src], true);
            }
          } else {
            dst[key] = src;
          }
        }
      }

      setHashKey(dst, h);
      return dst;
    }

    return function merge(dst) {
      return baseExtend(dst, [].slice.call(arguments, 1), true);
    }
  })();
}