merge two objects without adding new properties

Question

I have two JSON objects that I want to merge in such a way that only the values of the properties in the first object that already exist are updated.

I want to extend the first object with the second

var obj1 = {a:'apple', b:'banana', c:'cucumber'};
var obj2 = {a:'aarbei', b:'beet', d:'durian'};

and get this result

{a:'aarbei', b:'beet', c:'cucumber'};

instead of (which I get using $.extend)

{a:'aarbei', b:'beet', c:'cucumber', d:'durian'};

In reality my JSON objects can be much bigger and contain nested objects/arrays of unknown complexity

why did you chose that username?! i spit my whole coffee at the wall! — Philipp Sander
– Philipp Sander, Commented Feb 12, 2014 at 11:02
to save people from the possible risks of consuming hot beverages — mynameisnotallowed
– mynameisnotallowed, Commented Feb 12, 2014 at 11:03
I'd say that's not extending but a simple overwrite of obj1 with obj2 — KooiInc
– KooiInc, Commented Feb 12, 2014 at 11:06

dfsq · Accepted Answer · 2014-02-12 11:19:17Z

4

What about simple for loop:

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

For nested object you can wrap this code into recursive function:

function mergeObj(a, b) {
    for (var key in b) {
        if (key in a) {
            a[key] = typeof a[key] === 'object' && typeof b[key] === 'object' ? mergeObj(a[key], b[key]) : b[key];
        }
    }
    return a;
}

Demo: http://jsfiddle.net/rHUM6/

edited Feb 12, 2014 at 11:19

answered Feb 12, 2014 at 11:02

dfsq

193k26 gold badges244 silver badges261 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

mynameisnotallowed Over a year ago

This ignores the problem of nested objects/arrays

dfsq Over a year ago

Absolutely, you should have stated it in question!

mynameisnotallowed Over a year ago

I do. Read the last line

dfsq Over a year ago

Oh, no problem - we need recursion.

Kevin Bowersox · Accepted Answer · 2014-02-12 11:09:38Z

1

I took a different approach, trimming the unwanted properties from a copy of each object and then using those objects to extend a new object.

var obj1 = {a:'apple', b:'banana', c:'cucumber'};
var obj2 = {a:'aarbei', b:'beet', d:'durian'};
var keepProps = ["a", "b", "c"];

var trimmedObj1 = trim(obj1, keepProps);
var trimmedObj2 = trim(obj2, keepProps);

var obj3 = $.extend({}, trimmedObj1, trimmedObj2);
console.log(obj3);

function trim(obj, properties){
    var copy = $.extend({}, obj);
    for(x in obj){
        if(obj.hasOwnProperty(x) && properties.indexOf(x) == -1){
            delete copy[x];
        }
    }
    return copy;
}

JS Fiddle: http://jsfiddle.net/m8NCc/

answered Feb 12, 2014 at 11:09

Kevin Bowersox

94.6k19 gold badges164 silver badges198 bronze badges

1 Comment

mynameisnotallowed Over a year ago

I like this but also doesnt take into account the nested objects/arrays

SrikanthManian · Accepted Answer · 2014-02-12 11:11:42Z

1

This should work...

function mergeObjs () {
    for (var key in obj2) {
         if (obj1.hasOwnProperty(key)) {
             obj1[key] = obj2[key]
         }
    }
    return obj1;
}

var mergedObjs = mergeObjs();

edited Feb 12, 2014 at 11:11

answered Feb 12, 2014 at 11:05

SrikanthManian

1487 bronze badges

1 Comment

mynameisnotallowed Over a year ago

This ignores the problem of nested objects/arrays

Community · Accepted Answer · 2017-05-23 10:33:22Z

0

Javascript inherintance is not so complex.

If you have an object, let's say ObjectA like

function ObjectA () {
    this.a = "Hello";
    this.a = "World";
    this.c = 30;
}

Then you want to inherit this object :

function ObjectB () {
    ObjectA.call(this);// Call the super constructor
}
ObjectB.prototype = Object.create(ObjectA.prototype); // Inheritance
ObjectB.prototype.constructor = ObjectB;

Finally, you can acces and/or modify any property from ObjectA like :

var o = new ObjectB();
o.a = "Hi";

If you need to parse JSON object, see this (quoting myself :/).

edited May 23, 2017 at 10:33

CommunityBot

11 silver badge

answered Feb 12, 2014 at 11:08

Serge K.

5,3331 gold badge22 silver badges27 bronze badges

Collectives™ on Stack Overflow

merge two objects without adding new properties

4 Answers 4

Demo: http://jsfiddle.net/rHUM6/

4 Comments

1 Comment

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Demo: http://jsfiddle.net/rHUM6/

4 Comments

1 Comment

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related