How can I merge properties of two JavaScript objects dynamically?

JC Grubbs Source

I need to be able to merge two (very simple) JavaScript objects at runtime. For example I'd like to:

var obj1 = { food: 'pizza', car: 'ford' }
var obj2 = { animal: 'dog' }

obj1.merge(obj2);

//obj1 now has three properties: food, car, and animal

Does anyone have a script for this or know of a built in way to do this? I do not need recursion, and I do not need to merge functions, just methods on flat objects.

javascriptjavascript-objects

Answers

answered 10 years ago John Millikin #1

ECMAScript 2018 Standard Method

You would use object spread:

let merged = {...obj1, ...obj2};

/** There's no limit to the number of objects you can merge.
 *  Later properties overwrite earlier properties with the same name. */
const allRules = {...obj1, ...obj2, ...obj3};

ECMAScript 2015 (ES6) Standard Method

/* For the case in question, you would do: */
Object.assign(obj1, obj2);

/** There's no limit to the number of objects you can merge.
 *  All objects get merged into the first object. 
 *  Only the object in the first argument is mutated and returned.
 *  Later properties overwrite earlier properties with the same name. */
const allRules = Object.assign({}, obj1, obj2, obj3, etc);

(see MDN JavaScript Reference)


Method for ES5 and Earlier

for (var attrname in obj2) { obj1[attrname] = obj2[attrname]; }

Note that this will simply add all attributes of obj2 to obj1 which might not be what you want if you still want to use the unmodified obj1.

If you're using a framework that craps all over your prototypes then you have to get fancier with checks like hasOwnProperty, but that code will work for 99% of cases.

Example function:

/**
 * Overwrites obj1's values with obj2's and adds obj2's if non existent in obj1
 * @param obj1
 * @param obj2
 * @returns obj3 a new object based on obj1 and obj2
 */
function merge_options(obj1,obj2){
    var obj3 = {};
    for (var attrname in obj1) { obj3[attrname] = obj1[attrname]; }
    for (var attrname in obj2) { obj3[attrname] = obj2[attrname]; }
    return obj3;
}

answered 10 years ago ephemient #2

Prototype has this:

Object.extend = function(destination,source) {
    for (var property in source)
        destination[property] = source[property];
    return destination;
}

obj1.extend(obj2) will do what you want.

answered 10 years ago Avdi #3

jQuery also has a utility for this: http://api.jquery.com/jQuery.extend/.

Taken from the jQuery documentation:

// Merge options object into settings object
var settings = { validate: false, limit: 5, name: "foo" };
var options  = { validate: true, name: "bar" };
jQuery.extend(settings, options);

// Now the content of settings object is the following:
// { validate: true, limit: 5, name: "bar" }

The above code will mutate the existing object named settings.


If you want to create a new object without modifying either argument, use this:

var defaults = { validate: false, limit: 5, name: "foo" };
var options = { validate: true, name: "bar" };

/* Merge defaults and options, without modifying defaults */
var settings = $.extend({}, defaults, options);

// The content of settings variable is now the following:
// {validate: true, limit: 5, name: "bar"}
// The 'defaults' and 'options' variables remained the same.

answered 10 years ago Markus #4

I googled for code to merge object properties and ended up here. However since there wasn't any code for recursive merge I wrote it myself. (Maybe jQuery extend is recursive BTW?) Anyhow, hopefully someone else will find it useful as well.

(Now the code does not use Object.prototype :)

Code

/*
* Recursively merge properties of two objects 
*/
function MergeRecursive(obj1, obj2) {

  for (var p in obj2) {
    try {
      // Property in destination object set; update its value.
      if ( obj2[p].constructor==Object ) {
        obj1[p] = MergeRecursive(obj1[p], obj2[p]);

      } else {
        obj1[p] = obj2[p];

      }

    } catch(e) {
      // Property in destination object not set; create it and set its value.
      obj1[p] = obj2[p];

    }
  }

  return obj1;
}

An example

o1 = {  a : 1,
        b : 2,
        c : {
          ca : 1,
          cb : 2,
          cc : {
            cca : 100,
            ccb : 200 } } };

o2 = {  a : 10,
        c : {
          ca : 10,
          cb : 20, 
          cc : {
            cca : 101,
            ccb : 202 } } };

o3 = MergeRecursive(o1, o2);

Produces object o3 like

o3 = {  a : 10,
        b : 2,
        c : {
          ca : 10,
          cb : 20,
          cc : { 
            cca : 101,
            ccb : 202 } } };

answered 10 years ago Christoph #5

The given solutions should be modified to check source.hasOwnProperty(property) in the for..in loops before assigning - otherwise, you end up copying the properties of the whole prototype chain, which is rarely desired...

answered 10 years ago Tobi #6

The correct implementation in Prototype should look like this:

var obj1 = {food: 'pizza', car: 'ford'}
var obj2 = {animal: 'dog'}

obj1 = Object.extend(obj1, obj2);

answered 9 years ago philfreo #7

In MooTools, there's Object.merge():

Object.merge(obj1, obj2);

answered 9 years ago Algy #8

For not-too-complicated objects you could use JSON:

var obj1 = { food: 'pizza', car: 'ford' }
var obj2 = { animal: 'dog', car: 'chevy'}
var objMerge;

objMerge = JSON.stringify(obj1) + JSON.stringify(obj2);

// {"food": "pizza","car":"ford"}{"animal":"dog","car":"chevy"}

objMerge = objMerge.replace(/\}\{/, ","); //  \_ replace with comma for valid JSON

objMerge = JSON.parse(objMerge); // { food: 'pizza', animal: 'dog', car: 'chevy'}
// Of same keys in both objects, the last object's value is retained_/

Mind you that in this example "}{" must not occur within a string!

answered 8 years ago David Coallier #9

The best way for you to do this is to add a proper property that is non-enumerable using Object.defineProperty.

This way you will still be able to iterate over your objects properties without having the newly created "extend" that you would get if you were to create the property with Object.prototype.extend.

Hopefully this helps:

Object.defineProperty(Object.prototype, "extend", {
    enumerable: false,
    value: function(from) {
        var props = Object.getOwnPropertyNames(from);
        var dest = this;
        props.forEach(function(name) {
            if (name in dest) {
                var destination = Object.getOwnPropertyDescriptor(from, name);
                Object.defineProperty(dest, name, destination);
            }
        });
        return this;
    }
});

Once you have that working, you can do:

var obj = {
    name: 'stack',
    finish: 'overflow'
}
var replacement = {
    name: 'stock'
};

obj.extend(replacement);

I just wrote a blog post about it here: http://onemoredigit.com/post/1527191998/extending-objects-in-node-js

answered 7 years ago gossi #10

I extended David Coallier's method:

  • Added the possibility to merge multiple objects
  • Supports deep objects
  • override parameter (that's detected if the last parameter is a boolean)

If override is false, no property gets overridden but new properties will be added.

Usage: obj.merge(merges... [, override]);

Here is my code:

Object.defineProperty(Object.prototype, "merge", {
    enumerable: false,
    value: function () {
        var override = true,
            dest = this,
            len = arguments.length,
            props, merge, i, from;

        if (typeof(arguments[arguments.length - 1]) === "boolean") {
            override = arguments[arguments.length - 1];
            len = arguments.length - 1;
        }

        for (i = 0; i < len; i++) {
            from = arguments[i];
            if (from != null) {
                Object.getOwnPropertyNames(from).forEach(function (name) {
                    var descriptor;

                    // nesting
                    if ((typeof(dest[name]) === "object" || typeof(dest[name]) === "undefined")
                            && typeof(from[name]) === "object") {

                        // ensure proper types (Array rsp Object)
                        if (typeof(dest[name]) === "undefined") {
                            dest[name] = Array.isArray(from[name]) ? [] : {};
                        }
                        if (override) {
                            if (!Array.isArray(dest[name]) && Array.isArray(from[name])) {
                                dest[name] = [];
                            }
                            else if (Array.isArray(dest[name]) && !Array.isArray(from[name])) {
                                dest[name] = {};
                            }
                        }
                        dest[name].merge(from[name], override);
                    } 

                    // flat properties
                    else if ((name in dest && override) || !(name in dest)) {
                        descriptor = Object.getOwnPropertyDescriptor(from, name);
                        if (descriptor.configurable) {
                            Object.defineProperty(dest, name, descriptor);
                        }
                    }
                });
            }
        }
        return this;
    }
});

Examples and TestCases:

function clone (obj) {
    return JSON.parse(JSON.stringify(obj));
}
var obj = {
    name : "trick",
    value : "value"
};

var mergeObj = {
    name : "truck",
    value2 : "value2"
};

var mergeObj2 = {
    name : "track",
    value : "mergeObj2",
    value2 : "value2-mergeObj2",
    value3 : "value3"
};

assertTrue("Standard", clone(obj).merge(mergeObj).equals({
    name : "truck",
    value : "value",
    value2 : "value2"
}));

assertTrue("Standard no Override", clone(obj).merge(mergeObj, false).equals({
    name : "trick",
    value : "value",
    value2 : "value2"
}));

assertTrue("Multiple", clone(obj).merge(mergeObj, mergeObj2).equals({
    name : "track",
    value : "mergeObj2",
    value2 : "value2-mergeObj2",
    value3 : "value3"
}));

assertTrue("Multiple no Override", clone(obj).merge(mergeObj, mergeObj2, false).equals({
    name : "trick",
    value : "value",
    value2 : "value2",
    value3 : "value3"
}));

var deep = {
    first : {
        name : "trick",
        val : "value"
    },
    second : {
        foo : "bar"
    }
};

var deepMerge = {
    first : {
        name : "track",
        anotherVal : "wohoo"
    },
    second : {
        foo : "baz",
        bar : "bam"
    },
    v : "on first layer"
};

assertTrue("Deep merges", clone(deep).merge(deepMerge).equals({
    first : {
        name : "track",
        val : "value",
        anotherVal : "wohoo"
    },
    second : {
        foo : "baz",
        bar : "bam"
    },
    v : "on first layer"
}));

assertTrue("Deep merges no override", clone(deep).merge(deepMerge, false).equals({
    first : {
        name : "trick",
        val : "value",
        anotherVal : "wohoo"
    },
    second : {
        foo : "bar",
        bar : "bam"
    },
    v : "on first layer"
}));

var obj1 = {a: 1, b: "hello"};
obj1.merge({c: 3});
assertTrue(obj1.equals({a: 1, b: "hello", c: 3}));

obj1.merge({a: 2, b: "mom", d: "new property"}, false);
assertTrue(obj1.equals({a: 1, b: "hello", c: 3, d: "new property"}));

var obj2 = {};
obj2.merge({a: 1}, {b: 2}, {a: 3});
assertTrue(obj2.equals({a: 3, b: 2}));

var a = [];
var b = [1, [2, 3], 4];
a.merge(b);
assertEquals(1, a[0]);
assertEquals([2, 3], a[1]);
assertEquals(4, a[2]);


var o1 = {};
var o2 = {a: 1, b: {c: 2}};
var o3 = {d: 3};
o1.merge(o2, o3);
assertTrue(o1.equals({a: 1, b: {c: 2}, d: 3}));
o1.b.c = 99;
assertTrue(o2.equals({a: 1, b: {c: 2}}));

// checking types with arrays and objects
var bo;
a = [];
bo = [1, {0:2, 1:3}, 4];
b = [1, [2, 3], 4];

a.merge(b);
assertTrue("Array stays Array?", Array.isArray(a[1]));

a = [];
a.merge(bo);
assertTrue("Object stays Object?", !Array.isArray(a[1]));

a = [];
a.merge(b);
a.merge(bo);
assertTrue("Object overrides Array", !Array.isArray(a[1]));

a = [];
a.merge(b);
a.merge(bo, false);
assertTrue("Object does not override Array", Array.isArray(a[1]));

a = [];
a.merge(bo);
a.merge(b);
assertTrue("Array overrides Object", Array.isArray(a[1]));

a = [];
a.merge(bo);
a.merge(b, false);
assertTrue("Array does not override Object", !Array.isArray(a[1]));

My equals method can be found here: Object comparison in JavaScript

answered 7 years ago antony #11

I'm kind of getting started with JavaScript, so correct me if I'm wrong.

But wouldn't it be better if you could merge any number of objects? Here's how I do it using the native Arguments object.

The key to is that you can actually pass any number of arguments to a JavaScript function without defining them in the function declaration. You just can't access them without using the Arguments object.

function mergeObjects() (
    var tmpObj = {};

    for(var o in arguments) {
        for(var m in arguments[o]) {
            tmpObj[m] = arguments[o][m];
        }
    }
    return tmpObj;
}

answered 7 years ago RobKohr #12

Use:

//Takes any number of objects and returns one merged object
var objectMerge = function(){
    var out = {};
    if(!arguments.length)
        return out;
    for(var i=0; i<arguments.length; i++) {
        for(var key in arguments[i]){
            out[key] = arguments[i][key];
        }
    }
    return out;
}

It was tested with:

console.log(objectMerge({a:1, b:2}, {a:2, c:4}));

It results in:

{ a: 2, b: 2, c: 4 }

answered 7 years ago Mark #13

In Ext JS 4 it can be done as follows:

var mergedObject = Ext.Object.merge(object1, object2)

// Or shorter:
var mergedObject2 = Ext.merge(object1, object2)

See merge( object ) : Object.

answered 7 years ago user909278 #14

gossi's extension of David Coallier's method:

Check these two lines:

from = arguments[i];
Object.getOwnPropertyNames(from).forEach(function (name) {

One need to check "from" against null object... If for example merging an object that comes from an Ajax response, previously created on a server, an object property can have a value of "null", and in that case the above code generates an error saying:

"from" is not a valid object

So for example, wrapping the "...Object.getOwnPropertyNames(from).forEach..." function with an "if (from != null) { ... }" will prevent that error occurring.

answered 7 years ago vsync #15

function extend(o, o1, o2){
    if( !(o instanceof Object) ) o = {};

    copy(o, o1);
    if( o2 )
        copy(o, o2)

    function isObject(obj) {
        var type = Object.prototype.toString.call(obj);
        return obj === Object(obj) && type != '[object Array]' && type != '[object Function]';
    };

    function copy(a,b){
        // copy o2 to o
        for( var key in b )
            if( b.hasOwnProperty(key) ){
                if( isObject(b[key]) ){
                    if( !isObject(a[key]) )
                        a[key] = Object.assign({}, b[key]); 
                    else copy(a[key], b[key])
                }
                else
                    a[key] = b[key];
            }
    }

    return o;
};


var o1 = {a:{foo:1}, b:1},
    o2 = {a:{bar:2}, b:[1], c:()=>{}},
    newMerged = extend({}, o1, o2);
    
console.log( newMerged )
console.log( o1 )
console.log( o2 )

answered 7 years ago Emre Erkan #16

I need to merge objects today, and this question (and answers) helped me a lot. I tried some of the answers, but none of them fit my needs, so I combined some of the answers, added something myself and came up with a new merge function. Here it is:

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

Some example usages:

var t1 = {
    key1: 1,
    key2: "test",
    key3: [5, 2, 76, 21]
};
var t2 = {
    key1: {
        ik1: "hello",
        ik2: "world",
        ik3: 3
    }
};
var t3 = {
    key2: 3,
    key3: {
        t1: 1,
        t2: 2,
        t3: {
            a1: 1,
            a2: 3,
            a4: [21, 3, 42, "asd"]
        }
    }
};

console.log(merge(t1, t2));
console.log(merge(t1, t3));
console.log(merge(t2, t3));
console.log(merge(t1, t2, t3));
console.log(merge({}, t1, { key1: 1 }));

answered 7 years ago Snoozer Man #17

Based on Markus' and vsync' answer, this is an expanded version. The function takes any number of arguments. It can be used to set properties on DOM nodes and makes deep copies of values. However, the first argument is given by reference.

To detect a DOM node, the isDOMNode() function is used (see Stack Overflow question JavaScript isDOM — How do you check if a JavaScript Object is a DOM Object?)

It was tested in Opera 11, Firefox 6, Internet Explorer 8 and Google Chrome 16.

Code

function mergeRecursive() {

  // _mergeRecursive does the actual job with two arguments.
  var _mergeRecursive = function (dst, src) {
    if (isDOMNode(src) || typeof src !== 'object' || src === null) {
      return dst;
    }

    for (var p in src) {
      if (!src.hasOwnProperty(p))
        continue;
      if (src[p] === undefined)
        continue;
      if ( typeof src[p] !== 'object' || src[p] === null) {
        dst[p] = src[p];
      } else if (typeof dst[p]!=='object' || dst[p] === null) {
        dst[p] = _mergeRecursive(src[p].constructor===Array ? [] : {}, src[p]);
      } else {
        _mergeRecursive(dst[p], src[p]);
      }
    }
    return dst;
  }

  // Loop through arguments and merge them into the first argument.
  var out = arguments[0];
  if (typeof out !== 'object' || out === null)
    return out;
  for (var i = 1, il = arguments.length; i < il; i++) {
    _mergeRecursive(out, arguments[i]);
  }
  return out;
}

Some examples

Set innerHTML and style of a HTML Element

mergeRecursive(
  document.getElementById('mydiv'),
  {style: {border: '5px solid green', color: 'red'}},
  {innerHTML: 'Hello world!'});

Merge arrays and objects. Note that undefined can be used to preserv values in the lefthand array/object.

o = mergeRecursive({a:'a'}, [1,2,3], [undefined, null, [30,31]], {a:undefined, b:'b'});
// o = {0:1, 1:null, 2:[30,31], a:'a', b:'b'}

Any argument not beeing a JavaScript object (including null) will be ignored. Except for the first argument, also DOM nodes are discarded. Beware that i.e. strings, created like new String() are in fact objects.

o = mergeRecursive({a:'a'}, 1, true, null, undefined, [1,2,3], 'bc', new String('de'));
// o = {0:'d', 1:'e', 2:3, a:'a'}

If you want to merge two objects into a new (without affecting any of the two) supply {} as first argument

var a={}, b={b:'abc'}, c={c:'cde'}, o;
o = mergeRecursive(a, b, c);
// o===a is true, o===b is false, o===c is false

Edit (by ReaperSoon):

To also merge arrays

function mergeRecursive(obj1, obj2) {
  if (Array.isArray(obj2)) { return obj1.concat(obj2); }
  for (var p in obj2) {
    try {
      // Property in destination object set; update its value.
      if ( obj2[p].constructor==Object ) {
        obj1[p] = mergeRecursive(obj1[p], obj2[p]);
      } else if (Array.isArray(obj2[p])) {
        obj1[p] = obj1[p].concat(obj2[p]);
      } else {
        obj1[p] = obj2[p];
      }
    } catch(e) {
      // Property in destination object not set; create it and set its value.
      obj1[p] = obj2[p];
    }
  }
  return obj1;
}

answered 7 years ago Prabhakar Kasi #18

In YUI Y.merge should get the job done:

Y.merge(obj1, obj2, obj3....) 

answered 7 years ago Industrial #19

Note that underscore.js's extend-method does this in a one-liner:

_.extend({name : 'moe'}, {age : 50});
=> {name : 'moe', age : 50}

answered 6 years ago Paweł Szczur #20

Just if anyone is using Google Closure Library:

goog.require('goog.object');
var a = {'a': 1, 'b': 2};
var b = {'b': 3, 'c': 4};
goog.object.extend(a, b);
// Now object a == {'a': 1, 'b': 3, 'c': 4};

Similar helper function exists for array:

var a = [1, 2];
var b = [3, 4];
goog.array.extend(a, b); // Extends array 'a'
goog.array.concat(a, b); // Returns concatenation of array 'a' and 'b'

answered 6 years ago Michael Benin #21

function extend()
{ 
    var o = {}; 

    for (var i in arguments)
    { 
        var s = arguments[i]; 

        for (var i in s)
        { 
            o[i] = s[i]; 
        } 
    } 

    return o;
}

answered 6 years ago Andreas Linden #22

Just by the way, what you're all doing is overwriting properties, not merging...

This is how JavaScript objects area really merged: Only keys in the to object which are not objects themselves will be overwritten by from. Everything else will be really merged. Of course you can change this behaviour to not overwrite anything which exists like only if to[n] is undefined, etc...:

var realMerge = function (to, from) {

    for (n in from) {

        if (typeof to[n] != 'object') {
            to[n] = from[n];
        } else if (typeof from[n] == 'object') {
            to[n] = realMerge(to[n], from[n]);
        }
    }
    return to;
};

Usage:

var merged = realMerge(obj1, obj2);

answered 6 years ago Aram Kocharyan #23

This merges obj into a "default" def. obj has precedence for anything that exists in both, since obj is copied into def. Note also that this is recursive.

function mergeObjs(def, obj) {
    if (typeof obj == 'undefined') {
        return def;
    } else if (typeof def == 'undefined') {
        return obj;
    }
    for (var i in obj) {
        if (obj[i] != null && obj[i].constructor == Object) {
            def[i] = mergeObjs(def[i], obj[i]);
        } else {
            def[i] = obj[i];
        }
    }
    return def;
}

a = {x : {y : [123]}}
b = {x : {z : 123}}
console.log(mergeObjs(a, b));
// {x: {y : [123], z : 123}}

answered 6 years ago pagid #24

It's worth mentioning that the version from the 140byt.es collection is solving the task within minimum space and is worth a try for this purpose:

Code:

function m(a,b,c){for(c in b)b.hasOwnProperty(c)&&((typeof a[c])[0]=='o'?m(a[c],b[c]):a[c]=b[c])}

Usage for your purpose:

m(obj1,obj2);

Here's the original Gist.

answered 6 years ago jleviaguirre #25

A={a:1,b:function(){alert(9)}}
B={a:2,c:3}
A.merge = function(){for(var i in B){A[i]=B[i]}}
A.merge()

Result is: {a:2,c:3,b:function()}

answered 5 years ago Paul Spaulding #26

Here's my stab which

  1. Supports deep merge
  2. Does not mutate arguments
  3. Takes any number of arguments
  4. Does not extend the object prototype
  5. Does not depend on another library (jQuery, MooTools, Underscore.js, etc.)
  6. Includes check for hasOwnProperty
  7. Is short :)

    /*
        Recursively merge properties and return new object
        obj1 &lt;- obj2 [ &lt;- ... ]
    */
    function merge () {
        var dst = {}
            ,src
            ,p
            ,args = [].splice.call(arguments, 0)
        ;
    
        while (args.length > 0) {
            src = args.splice(0, 1)[0];
            if (toString.call(src) == '[object Object]') {
                for (p in src) {
                    if (src.hasOwnProperty(p)) {
                        if (toString.call(src[p]) == '[object Object]') {
                            dst[p] = merge(dst[p] || {}, src[p]);
                        } else {
                            dst[p] = src[p];
                        }
                    }
                }
            }
        }
    
       return dst;
    }
    

Example:

a = {
    "p1": "p1a",
    "p2": [
        "a",
        "b",
        "c"
    ],
    "p3": true,
    "p5": null,
    "p6": {
        "p61": "p61a",
        "p62": "p62a",
        "p63": [
            "aa",
            "bb",
            "cc"
        ],
        "p64": {
            "p641": "p641a"
        }
    }
};

b = {
    "p1": "p1b",
    "p2": [
        "d",
        "e",
        "f"
    ],
    "p3": false,
    "p4": true,
    "p6": {
        "p61": "p61b",
        "p64": {
            "p642": "p642b"
        }
    }
};

c = {
    "p1": "p1c",
    "p3": null,
    "p6": {
        "p62": "p62c",
        "p64": {
            "p643": "p641c"
        }
    }
};

d = merge(a, b, c);


/*
    d = {
        "p1": "p1c",
        "p2": [
            "d",
            "e",
            "f"
        ],
        "p3": null,
        "p5": null,
        "p6": {
            "p61": "p61b",
            "p62": "p62c",
            "p63": [
                "aa",
                "bb",
                "cc"
            ],
            "p64": {
                "p641": "p641a",
                "p642": "p642b",
                "p643": "p641c"
            }
        },
        "p4": true
    };
*/

answered 5 years ago Paul #27

You could assign every object a default merge (perhaps 'inherit' a better name) method:

It should work with either objects or instantiated functions.

The below code handles overriding the merged values if so desired:

Object.prototype.merge = function(obj, override) {
// Don't override by default

    for (var key in obj) {
        var n = obj[key];
        var t = this[key];
        this[key] = (override && t) ? n : t;
    };

};

Test data is below:

var Mammal = function () {
    this.eyes = 2;
    this.thinking_brain = false;
    this.say = function () {
    console.log('screaming like a mammal')};
}

var Human = function () {
    this.thinking_brain = true;
    this.say = function() {console.log('shouting like a human')};
}

john = new Human();

// Extend mammal, but do not override from mammal
john.merge(new Mammal());
john.say();

// Extend mammal and override from mammal
john.merge(new Mammal(), true);
john.say();

answered 5 years ago bravedick #28

My way:

function mergeObjects(defaults, settings) {
    Object.keys(defaults).forEach(function(key_default) {
        if (typeof settings[key_default] == "undefined") {
            settings[key_default] = defaults[key_default];
        } else if (isObject(defaults[key_default]) && isObject(settings[key_default])) {
            mergeObjects(defaults[key_default], settings[key_default]);
        }
    });

    function isObject(object) {
        return Object.prototype.toString.call(object) === '[object Object]';
    }

    return settings;
}

:)

answered 5 years ago Egor Kloos #29

I've used Object.create() to keep the default settings (utilising __proto__ or Object.getPrototypeOf() ).

function myPlugin( settings ){
    var defaults = {
        "keyName": [ "string 1", "string 2" ]
    }
    var options = Object.create( defaults );
    for (var key in settings) { options[key] = settings[key]; }
}
myPlugin( { "keyName": ["string 3", "string 4" ] } );

This way I can always 'concat()' or 'push()' later.

var newArray = options['keyName'].concat( options.__proto__['keyName'] );

Note: You'll need to do a hasOwnProperty check before concatenation to avoid duplication.

answered 5 years ago AndreasE #30

Similar to jQuery extend(), you have the same function in AngularJS:

// Merge the 'options' object into the 'settings' object
var settings = {validate: false, limit: 5, name: "foo"};
var options  = {validate: true, name: "bar"};
angular.extend(settings, options);

answered 5 years ago devmao #31

With Underscore.js, to merge an array of objects do:

var arrayOfObjects = [ {a:1}, {b:2, c:3}, {d:4} ];
_(arrayOfObjects).reduce(function(memo, o) { return _(memo).extend(o); });

It results in:

Object {a: 1, b: 2, c: 3, d: 4}

answered 4 years ago Ryan Walls #32

For those using Node.js, there's an NPM module: node.extend

Install:

npm install node.extend

Usage:

var extend = require('node.extend');
var destObject = extend(true, {}, sourceObject);
// Where sourceObject is the object whose properties will be copied into another.

answered 4 years ago antitoxic #33

There's a library called deepmerge on GitHub: That seems to be getting some traction. It's a standalone, available through both the npm and bower package managers.

I would be inclined to use or improve on this instead of copy-pasting code from answers.

answered 4 years ago NanoWizard #34

The Harmony ECMAScript 2015 (ES6) specifies Object.assign which will do this.

Object.assign(obj1, obj2);

Current browser support is getting better, but if you're developing for browsers that don't have support, you can use a polyfill.

answered 4 years ago Scdev #35

This solution creates a new object and is able to handle multiple objects.

Furthermore, it is recursive and you can chose weather you want to overwrite Values and Objects.

    function extendObjects() {

        var newObject        = {};
        var overwriteValues  = false;
        var overwriteObjects = false;

        for ( var indexArgument = 0; indexArgument < arguments.length; indexArgument++ ) {

            if ( typeof arguments[indexArgument] !== 'object' ) {

                if ( arguments[indexArgument] == 'overwriteValues_True' ) {

                    overwriteValues = true;            
                } else if ( arguments[indexArgument] == 'overwriteValues_False' ) {

                    overwriteValues = false;                             
                } else if ( arguments[indexArgument] == 'overwriteObjects_True' ) {

                    overwriteObjects = true;     
                } else if ( arguments[indexArgument] == 'overwriteObjects_False' ) {

                    overwriteObjects = false; 
                }

            } else {

                extendObject( arguments[indexArgument], newObject, overwriteValues, overwriteObjects );
            }

        }

        function extendObject( object, extendedObject, overwriteValues, overwriteObjects ) {

            for ( var indexObject in object ) {

                if ( typeof object[indexObject] === 'object' ) {

                    if ( typeof extendedObject[indexObject] === "undefined" || overwriteObjects ) {
                        extendedObject[indexObject] = object[indexObject];
                    }

                    extendObject( object[indexObject], extendedObject[indexObject], overwriteValues, overwriteObjects );

                } else {

                    if ( typeof extendedObject[indexObject] === "undefined" || overwriteValues ) {
                        extendedObject[indexObject] = object[indexObject];
                    }

                }

            }     

            return extendedObject;

        }

        return newObject;
    }

    var object1           = { a : 1, b : 2, testArr : [888, { innArr : 1 }, 777 ], data : { e : 12, c : { lol : 1 }, rofl : { O : 3 } } };
    var object2           = { a : 6, b : 9, data : { a : 17, b : 18, e : 13, rofl : { O : 99, copter : { mao : 1 } } }, hexa : { tetra : 66 } };
    var object3           = { f : 13, g : 666, a : 333, data : { c : { xD : 45 } }, testArr : [888, { innArr : 3 }, 555 ]  };

    var newExtendedObject = extendObjects( 'overwriteValues_False', 'overwriteObjects_False', object1, object2, object3 );

Contents of newExtendedObject:

{"a":1,"b":2,"testArr":[888,{"innArr":1},777],"data":{"e":12,"c":{"lol":1,"xD":45},"rofl":{"O":3,"copter":{"mao":1}},"a":17,"b":18},"hexa":{"tetra":66},"f":13,"g":666}

Fiddle: http://jsfiddle.net/o0gb2umb/

answered 4 years ago appsmatics #36

The following two are probably a good starting point. lodash also has a customizer function for those special needs!

_.extend (http://underscorejs.org/#extend)
_.merge (https://lodash.com/docs#merge)

answered 3 years ago T.Todua #37

Another method:

function concat_collection(obj1, obj2) {
    var i;
    var arr = new Array();

    var len1 = obj1.length;
    for (i=0; i<len1; i++) {
        arr.push(obj1[i]);
    }

    var len2 = obj2.length;
    for (i=0; i<len2; i++) {
        arr.push(obj2[i]);
    }

    return arr;
}

var ELEMENTS = concat_collection(A,B);
for(var i = 0; i < ELEMENTS.length; i++) {
    alert(ELEMENTS[i].value);
}

answered 3 years ago Etherealone #38

I use the following which is in pure JavaScript. It starts from the right-most argument and combines them all the way up to the first argument. There is no return value, only the first argument is modified and the left-most parameter (except the first one) has the highest weight on properties.

var merge = function() {
  var il = arguments.length;

  for (var i = il - 1; i > 0; --i) {
    for (var key in arguments[i]) {
      if (arguments[i].hasOwnProperty(key)) {
        arguments[0][key] = arguments[i][key];
      }
    }
  }
};

answered 3 years ago Dinusha #39

You can simply use jQuery extend

var obj1 = { val1: false, limit: 5, name: "foo" };
var obj2 = { val2: true, name: "bar" };

jQuery.extend(obj1, obj2);

Now obj1 contains all the values of obj1 and obj2

answered 3 years ago Vikash Pandey #40

If you are using Dojo Toolkit then the best way to merge two object is using a mixin.

Below is the sample for Dojo Toolkit mixin:

// Dojo 1.7+ (AMD)
require(["dojo/_base/lang"], function(lang){
  var a = { b:"c", d:"e" };
  lang.mixin(a, { d:"f", g:"h" });
  console.log(a); // b:c, d:f, g:h
});

// Dojo < 1.7
var a = { b:"c", d:"e" };
dojo.mixin(a, { d:"f", g:"h" });
console.log(a); // b:c, d:f, g:h

For more details, please mixin.

answered 3 years ago Sherali Turdiyev #41

You can merge objects through following my method

var obj1 = { food: 'pizza', car: 'ford' };
var obj2 = { animal: 'dog' };

var result = mergeObjects([obj1, obj2]);

console.log(result);
document.write("result: <pre>" + JSON.stringify(result, 0, 3) + "</pre>");

function mergeObjects(objectArray) {
    if (objectArray.length) {
        var b = "", i = -1;
        while (objectArray[++i]) {
            var str = JSON.stringify(objectArray[i]);
            b += str.slice(1, str.length - 1);
            if (objectArray[i + 1]) b += ",";
        }
        return JSON.parse("{" + b + "}");
    }
    return {};
}

answered 3 years ago Reza Roshan #42

Object.assign()

ECMAScript 2015 (ES6)

This is a new technology, part of the ECMAScript 2015 (ES6) standard. This technology's specification has been finalized, but check the compatibility table for usage and implementation status in various browsers.

The Object.assign() method is used to copy the values of all enumerable own properties from one or more source objects to a target object. It will return the target object.

var o1 = { a: 1 };
var o2 = { b: 2 };
var o3 = { c: 3 };

var obj = Object.assign(o1, o2, o3);
console.log(obj); // { a: 1, b: 2, c: 3 }
console.log(o1);  // { a: 1, b: 2, c: 3 }, target object itself is changed.

answered 3 years ago Eugene Tiurin #43

Merge properties of N objects in one line of code

An Object.assign method is part of the ECMAScript 2015 (ES6) standard and does exactly what you need. (IE not supported)

var clone = Object.assign({}, obj);

The Object.assign() method is used to copy the values of all enumerable own properties from one or more source objects to a target object.

Read more...

The polyfill to support older browsers:

if (!Object.assign) {
  Object.defineProperty(Object, 'assign', {
    enumerable: false,
    configurable: true,
    writable: true,
    value: function(target) {
      'use strict';
      if (target === undefined || target === null) {
        throw new TypeError('Cannot convert first argument to object');
      }

      var to = Object(target);
      for (var i = 1; i < arguments.length; i++) {
        var nextSource = arguments[i];
        if (nextSource === undefined || nextSource === null) {
          continue;
        }
        nextSource = Object(nextSource);

        var keysArray = Object.keys(nextSource);
        for (var nextIndex = 0, len = keysArray.length; nextIndex < len; nextIndex++) {
          var nextKey = keysArray[nextIndex];
          var desc = Object.getOwnPropertyDescriptor(nextSource, nextKey);
          if (desc !== undefined && desc.enumerable) {
            to[nextKey] = nextSource[nextKey];
          }
        }
      }
      return to;
    }
  });
}

answered 3 years ago Raphaël #44

You should use lodash's defaultsDeep

_.defaultsDeep({ 'user': { 'name': 'barney' } }, { 'user': { 'name': 'fred', 'age': 36 } });
// → { 'user': { 'name': 'barney', 'age': 36 } }

answered 3 years ago Yaki Klein #45

A possible way to achieve this is the following.

if (!Object.prototype.merge){
    Object.prototype.merge = function(obj){
        var self = this;
        Object.keys(obj).forEach(function(key){
            self[key] = obj[key]
        });
    }
};

I don't know if it's better then the other answers. In this method you add the merge function to Objects prototype. This way you can call obj1.merge(obj2);

Note : you should validate your argument to see if its an object and 'throw' a proper Error. If not Object.keys will 'throw' an 'Error'

answered 3 years ago Nishant Kumar #46

Here what I used in my codebase to merge.

function merge(to, from) {
  if (typeof to === 'object' && typeof from === 'object') {
    for (var pro in from) {
      if (from.hasOwnProperty(pro)) {
        to[pro] = from[pro];
      }
    }
  }
  else{
      throw "Merge function can apply only on object";
  }
}

answered 2 years ago trincot #47

If you need a deep merge that will also "merge" arrays by concatenating them in the result, then this ES6 function might be what you need:

function deepMerge(a, b) {
    // If neither is an object, return one of them:
    if (Object(a) !== a && Object(b) !== b) return b || a;
    // Replace remaining primitive by empty object/array
    if (Object(a) !== a) a = Array.isArray(b) ? [] : {};
    if (Object(b) !== b) b = Array.isArray(a) ? [] : {};
    // Treat arrays differently:
    if (Array.isArray(a) && Array.isArray(b)) {
        // Merging arrays is interpreted as concatenation of their deep clones:
        return [...a.map(v => deepMerge(v)), ...b.map(v => deepMerge(v))];
    } else {
        // Get the keys that exist in either object
        var keys = new Set([...Object.keys(a),...Object.keys(b)]);
        // Recurse and assign to new object
        return Object.assign({}, ...Array.from(keys,
            key => ({ [key]: deepMerge(a[key], b[key]) }) ));
    }
}

// Sample data for demo:
var a = {
    groups: [{
        group: [{
            name: 'John',
            age: 12
        },{
            name: 'Mary',
            age: 20
        }],
        groupName: 'Pair'
    }],
    config: {
        color: 'blue',
        range: 'far'
    }
};


var b = {
    groups: [{
        group: [{
            name: 'Bill',
            age: 15
        }],
        groupName: 'Loner'
    }],
    config: {
        range: 'close',
        strength: 'average'
    }
};

var merged = deepMerge(a, b);

console.log(merged);
.as-console-wrapper { max-height: 100% !important; top: 0; }

Note that if only one argument is passed to this function, it acts as a deep clone function.

answered 2 years ago Jaime Asm #48

You can use object spread properties—currently a stage 3 ECMAScript proposal.

const obj1 = { food: 'pizza', car: 'ford' };
const obj2 = { animal: 'dog' };

const obj3 = { ...obj1, ...obj2 };
console.log(obj3);

answered 2 years ago mitch3ls #49

You can do the following in EcmaScript2016

Correction: it's a stage 3 proposal, still it has always worked for me

const objA = {
  attrA: 'hello',
  attrB: true
}

const objB = {
  attrC: 2
}

const mergedObj = {...objA, ...objB}

answered 1 year ago Bekim Bacaj #50

The Merge Of JSON Compatible JavaScript Objects

I encourage the use and utilization of nondestructive methods that don't modify the original source, 'Object.assign' is a destructive method and it also happens to be not so production friendly because it stops working on earlier browsers and you have no way of patching it cleanly, with an alternative.

Merging JS Objects will always be out of reach, or incomplete, whatever the solution. But merging JSON compliant compatible objects is just one step away from being able to write a simple and portable piece of code of a nondestructive method of merging series of JS Objects into a returned master containing all the unique property-names and their corresponding values synthesized in a single master object for the intended purpose.

Having in mind that MSIE8 is the first browser to have added a native support for the JSON object is a great relief, and reusing the already existing technology, is always a welcomed opportunity.

Restricting your code to JSON complant standard objects, is more of an advantage, than a restriction - since these objects can also be transmitted over the Internet. And of course for those who would like a deeper backward compatibility there's always a json plug., whose methods can easily be assigned to a JSON variable in the outer code without having to modify or rewrite the method in use.

function Merge( ){
    var a = [].slice.call( arguments ), i = 0;
        while( a[i] )a[i] = JSON.stringify( a[i++] ).slice( 1,-1 );
        return JSON.parse( "{"+ a.join() +"}" );
    }

(Of course one can always give it a more meaningful name, which I haven't decided yet; should probably name it JSONmerge)

The use case:

var master = Merge( obj1, obj2, obj3, ...objn );

Now, contrary to the Object.assign this leaves all objects untouched and in their original state (in case you've done something wrong and need to reorder the merging objects or be able to use them separately for some other operation before merging them again).

Tthe number of the Merge arguments is also limited only by the arguments length limit [which is huge]. The natively supported JSON parse / stringify is already machine optimized, meaning: it should be faster than any scripted form of JS loop. The iteration over given arguments, is being done using the while - proven to be the fastest loop in JS.

It doesn't harm to briefly mention the fact we already know that duplicate properties of the unique object labels (keys) will be overwritten by the later object containing the same key label, which means you are in control of which property is taking over the previous by simply ordering or reordering the arguments list. And the benefit of getting a clean and updated master object with no dupes as a final output.

answered 1 year ago toster-cx #51

ES5 compatible native one-liner:

var merged = [obj1, obj2].reduce(function(a, o) { for(k in o) a[k] = o[k]; return a; }, {})

answered 1 year ago Samad Aghaei #52

<pre>
/**
This script can merge two multi dimensional associative array/objects in javascript by comparing given object with its reference and 
will remove additional given keys, adding missed parameteres and also validating values without overhead. Also it will return the default values if no input presented with re-usable reference!
Tested on IE8 and greater.
**/
var module = (function(){
    //To make our reference variable onchangable, have to put it into a function which is fster and more efficient than "JSON.parse(JSON.stringify(VARIABLE))"
    var _defs = function(){
            return {
                   //string, number and boolean are actually regex based validation keys on input values.
                a: ["string", 'Defaul value for "a"'],
                b: ["number", 300],
                c: ["boolean", true],
                d: {
                  da: ["boolean", true],
                  db: ["string", 'Defaul value for "db"'],
                  dc: {
                    dca: ["number", 200],
                    dcb: ["string", 'Default value for "dcb"'],
                    dcc: ["number", 500],
                    dcd: ["boolean", true]
                  },
                  dce: ["string", 'Default value for "dce"'],
                },
                e: ["number", 200],
                f: ["boolean", 0],
                g: ["", 'This is an internal extra parameter']
            }
        }

        var _validation = {
                number: function (defaultValue, userValue) {
                  if(/^[0-9]+$/.test(userValue)) //Only numbers allowed
                    return userValue;
                  else return defaultValue;
                },
                string: function (defaultValue, userValue) {
                  if(/^[a-zA-Z\s]*$/.test(userValue)) //Only A to Z case insentitive with space aloowed.
                    return userValue;
                  else return defaultValue;
                },
                boolean: function (defaultValue, userValue) {
                  if(typeof userValue === 'boolean') //True or False or 0 ,1
                    return userValue;
                  else return defaultValue;
                }
        }

        var _uniqueMerge = function(opts, _ref){
                for(var key in _ref)
                    if (_ref && _ref[key] && _ref[key].constructor && _ref[key].constructor === Object)
                      _ref[key] = _uniqueMerge((opts ? opts[key] : null ), _ref[key] );
                    else if(opts && opts.hasOwnProperty(key))
                      _ref[key] = _validation[_ref[key][0]](_ref[key][1], opts[key]); //or without validation on user enties => ref[key] = obj[key]
                    else _ref[key] = _ref[key][1];
                return _ref;
        }
        var _get = function(inputs){
            return _uniqueMerge(inputs, _defs());
        }
        return {
            options: function(){
            return _get(arguments[0] || null); // for more safety and control on number of input variables! used --> ( arguments[0] || null )
            }
        }
})();


//How to use it:    

input_one = { 
    a : "Hello World", 
  //b : ["number", 400], //User missed this parameter
    c: "Hi",
    d : {
        da : false,
        db : "Hellow! World", // ! is not allowed
        dc : {
            dca : 10,
            dcb : "My String",
            dcc: "3thString",
            dcd : false
      },
      dce: "ANOTHER STRING",
    },
    e: 40,
    f: true,
    z: 'x'
};
console.log( JSON.stringify( module.options(input_one), null ,2 ) );
//Output:
/*
{
  "a": "Hello World",
  "b": 300,
  "c": true,
  "d": {
    "da": false,
    "db": "Defaul value for \"db\"",
    "dc": {
      "dca": 10,
      "dcb": "My String",
      "dcc": 500,
      "dcd": false
    },
    "dce": "ANOTHER STRING"
  },
  "e": 40,
  "f": true,
  "g": "This is an internal extra parameter"
}
*/
input_two = { 
    a : 32,
  //b : ["number", 400], //User missed this parameter
    c: "Hi",
    d : {
        da : false,
        db : "HelloWorld",
        dc : {
            dca : 10,
            dcb : "My String",
            dcd : false
      },
      dce: 73,
    }
};
console.log( JSON.stringify( module.options(input_two), null ,2 ) );
//output
/*
{
  "a": "Defaul value for \"a\"",
  "b": 300,
  "c": true,
  "d": {
    "da": false,
    "db": "HelloWorld",
    "dc": {
      "dca": 10,
      "dcb": "My String",
      "dcc": 500,
      "dcd": false
    },
    "dce": "Default value for \"dce\""
  },
  "e": 200,
  "f": 0,
  "g": "This is an internal extra parameter"
}
*/
//Empty input will return the default values!
console.log( JSON.stringify( module.options(), null ,2 ) );     
//Output
/*  
{
  "a": "Defaul value for \"a\"",
  "b": 300,
  "c": true,
  "d": {
    "da": true,
    "db": "Defaul value for \"db\"",
    "dc": {
      "dca": 200,
      "dcb": "Default value for \"dcb\"",
      "dcc": 500,
      "dcd": true
    },
    "dce": "Default value for \"dce\""
  },
  "e": 200,
  "f": 0,
  "g": "This is an internal extra parameter"
}
*/
</pre>

answered 1 year ago Imamudin Naseem #53

use object.assign

Object.prototype.assign = Object.assign && function () {
    var a = [];
    for (var _i = 0; _i < arguments.length; _i++) {
        a[_i] = arguments[_i];
    }
    var src = a.slice(1);
    var target = a[0];
    for (var o in src) {
        if (src.hasOwnProperty(o)) {
            var keys = Object.keys(src[o]);
            var _src = src[o];
            for (var k in keys) {
                if (keys.hasOwnProperty(k)) {
                    var _key = keys[k];
                    target[_key] = _src[_key];
                }
            }
        }
    }
    return target;
};

answered 6 months ago Legends #54

Merging objects is simple.

var obj1 = { food: 'pizza', car: 'ford' }
var obj2 = { animal: 'dog', car: 'BMW' }
var obj3 = {a: "A"}


var mergedObj = Object.assign(obj1,obj2,obj3)

console.log(mergedObj);

The objects are merged from right to left, this means that objects which have identical properties as the objects to their right will be overriden.

In this example obj2.car overrides obj1.car

answered 5 months ago Logan #55

Wow.. this is the first StackOverflow post I've seen with multiple pages. Apologies for adding another "answer"

This method is for ES5 & Earlier - there are plenty of other answers addressing ES6.

I did not see any "deep" object merging utilizing the arguments property. Here is my answer - compact & recursive, allowing unlimited object arguments to be passed:

function extend() {
    for (var o = {}, i = 0; i < arguments.length; i++) {
        // if (arguments[i].constructor !== Object) continue;
        for (var k in arguments[i]) {
            if (arguments[i].hasOwnProperty(k)) {
                o[k] = arguments[i][k].constructor === Object ? extend(o[k] || {}, arguments[i][k]) : arguments[i][k];
            }
        }
    }
    return o;
}

The portion that is commented out is optional .. it will simply skip arguments passed that are not objects (preventing errors).

Example:

extend({
    api: 1,
    params: {
        query: 'hello'
    }
}, {
    params: {
        query: 'there'
    }
});

// outputs {api: 1, params: {query: 'there'}}

This answer is now but a drop in the ocean ...

answered 4 months ago aircraft #56

We can crate a empty object, and combine them by for-loop:

var obj1 = {
  id: '1',
  name: 'name'
}

var obj2 = {
  c: 'c',
  d: 'd'
}

var obj3 = {}

for (var attrname in obj1) { obj3[attrname] = obj1[attrname]; }
for (var attrname in obj2) { obj3[attrname] = obj2[attrname]; }


console.log( obj1, obj2, obj3)

answered 6 days ago TinhNQ #57

var obj1 = { food: 'pizza', car: 'ford' }
var obj2 = { animal: 'dog' }

// result
result: {food: "pizza", car: "ford", animal: "dog"}

Using jQuery.extend() - Link

// Merge obj1 & obj2 to result
var result1 = $.extend( {}, obj1, obj2 );

Using _.merge() - Link

// Merge obj1 & obj2 to result
var result2 = _.merge( {}, obj1, obj2 );

Using _.extend() - Link

// Merge obj1 & obj2 to result
var result3 = _.extend( {}, obj1, obj2 );

Using Object.assign() ECMAScript 2015 (ES6) - Link

// Merge obj1 & obj2 to result
var result4 = Object.assign( {}, obj1, obj2 );

Output of all

obj1: { animal: 'dog' }
obj2: { food: 'pizza', car: 'ford' }
result1: {food: "pizza", car: "ford", animal: "dog"}
result2: {food: "pizza", car: "ford", animal: "dog"}
result3: {food: "pizza", car: "ford", animal: "dog"}
result4: {food: "pizza", car: "ford", animal: "dog"}

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