How to duplicate object properties in another object?

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Given the object:

var firstObject = {
    key1 : 'value1',
    key2 : 'value2'
};

how can I copy the properties inside another object (secondObject) like this:

var secondObject = {
    key1 : 'value1',
    key2 : 'value2',
    key3 : 'value3',
    key4 : 'value4'
};

using a reference to the firstObject? Something like this:

var secondObject = {
    firstObject,
    key3 : 'value3',
    key4 : 'value4'
};

(this doesn't work... I put it just to show in big lines how I would like to structure the code).

Is a solution possible without using any JavaScript frameworks?

for(var k in firstObject) secondObject[k]=firstObject[k];

How to duplicate object properties in another object?, An object is a collection of properties, and a property is an looping through the original object and copying each property one after the other. Javascript Front End Technology Object Oriented Programming The Object.assign() method can be used to copy the values of all of the object's own properties(enumerable only) from one or more source objects to a target object. For example, to copy all the properties of a source object onto a target object, you can use the following code −

Taking a cue from @Bardzuśny's answer here, ES6 has delivered a native solution: the Object.assign() function!

Usage is simple:

Object.assign(secondObject, firstObject);

That's it!

Support right now is obviously poor; only Firefox (34+) supports it out-of-the-box, while Chrome (45+) and Opera (32+) require the 'experimental flag' to be set.

Support is improving, with the lastest versions of Chrome, Firefox, Opera, Safari and Edge supporting it (IE notably has no support.) Transpilers are available as well, like Babel and Traceur. See here for more details.

4 different techniques for copying objects in JavaScript, How do I copy one object to another in JavaScript? In a deep copy, all the properties (including reference) of the source object are copied as values to the target object. There is no sharing of the reference between the source and target objects

Per ES6 - Spread syntax:

You can simply use:

const thirdObject = {
   ...firstObject,
   ...secondObject   
}

This avoids problems of passing these objects by reference.

Additionally it takes care of objects that have deep nesting.

Copying Objects in JavaScript ― Scotch.io, The Object.assign() method can be used to copy the values of all of the object's own properties(enumerable only) from one or more source  Copy model object properties by using the property pane. Select the object you want to copy properties from. Click Copy properties in the property pane. The mouse pointer changes into a paintbrush, and you can select in the property pane which properties Select the objects you want to copy

Loop through the properties of the first object and assign them to the second object, like this:

var firstObject = {
    key1 : 'value1',
    key2 : 'value2'
};

var secondObject = {
    key3 : 'value3',
    key4 : 'value4'
};

for (var prop in firstObject) {
    if (firstObject.hasOwnProperty(prop)) {
        secondObject[prop] = firstObject[prop];
    }
}

The for-in loop isn't enough; you need hasOwnProperty. See http://bonsaiden.github.com/JavaScript-Garden/#object.forinloop for a detailed explanation of why.

How to add a new item to an object at a specific position with vanilla , Both methodologies can be equivalently used to copy/merge the enumerable properties of an object to another object. Problem with these two  Object.assign. The Object.assign() method can be used to copy the values of all enumerable own properties from one or more source objects to a target object, and it will return the target object. var obj = { foo: "foo", bar: "bar" }; var clonedObj = Object.assign({}, obj); // Object { foo: "foo", bar: "bar" } Using the spread syntax or Object. assign is a standard way of copying an object in JavaScript.

Playing the necromancer here, because ES5 brought us Object.keys(), with potential to save us from all these .hasOwnProperty() checks.

Object.keys(firstObject).forEach(function(key) {
  secondObject[key] = firstObject[key];
});

Or, wrapping it into a function (limited "copy" of lodash _.assign()):

function assign(object, source) {
  Object.keys(source).forEach(function(key) {
    object[key] = source[key];
  });
}

assign(secondObject, firstObject); // assign firstObject properties to secondObject

Object.keys() is relatively new method, most notably: not available in IE < 9. The same actually goes for .forEach() array method, which I used in place of regular for loop.

Luckily, there is es5-shim available for these ancient browsers, which will polyfill many ES5 features (including those two).

(I'm all for polyfills as opposed to holding back from using cool, new language features.)

How to copy all the values from one JSONObject to another?, When we assign the object to other variables, only the memory address is copied​. Once we change the property of a or b , we are changing the  Click Home tab > Properties panel > Match Properties. Find Select the object from which you want to copy properties. If you want to specify which properties are copied, enter s (Settings). In the Property Settings dialog box, clear the properties that you do not want copied, and click OK. Select the objects to which you want to copy the properties, and press Enter

How to deep clone a JavaScript object, Cloning an object in JavaScript a task that is almost always used in any project we need to recursively detect if the value is yet another object (object literal in if the value is a nested object, recursively copy all it's properties Click Home tabClipboard panelMatch Properties. Find Select the object from which you want to copy properties. If you want to specify which properties are copied, enter s (Settings). In the Property Settings dialog box, clear the properties that you do not want copied, and click OK. Select the objects to which you want to copy the properties, and press Enter

How to duplicate Javascript object properties in another object?, But no worries, here are 3 ways for you to clone an object Spread on the other hand is an operator which copies properties of one object into a new object. Following code would explain how to copy all properties from one object to another using reflection: public static void CopyProperties (object objSource, object objDestination)

Different methods to copy an object in JavaScript, In other words, properties of all arguments starting from the second are copied into the first object. The call returns dest . For instance, we can use  The naive way of copying objects is looping through the original object and copying each property one after the other. Let's take a look at this code: function copy ( mainObj ) { let objCopy = { } ; // objCopy will store a copy of the mainObj let key ; for ( key in mainObj ) { objCopy [ key ] = mainObj [ key ] ; // copies each property to the objCopy object } return objCopy ; } const mainObj = { a : 2 , b : 5 , c : { x : 7 , y : 4 , } , } console . log ( copy ( mainObj ) ) ;

Comments
  • Answered here: stackoverflow.com/questions/171251/…
  • The question is, do you want a shallow or a deep copy? If deep, how deep?
  • FWIW, they're called "properties," not "attributes."
  • Here's something really ugly that works nonetheless (not actually recommended! Just a one-liner proof-of-concept): secondObject = JSON.parse('{' + JSON.stringify(firstObject).match(/^.(.*).$/)[1] + ',' + JSON.stringify(secondObject).match(/^.(.*).$/)[1] + '}');
  • @T.J.Crowder: I corrected the question... thanks.
  • @BenLee, what you're missing here is that Igor has shown the exact use he has for it, in which hasOwnProperty is useless. While I find your pointer useful, I consider the idea of applying any rules to any situation harmful and unwise. Like all these pattern-driven development practices that are going on, so don't take it personal…
  • @MichaelKrelin-hacker, what you're missing here is that StackOverflow is not just for the benefit of the OP. It's used as a reference for future visitors who may have slightly different use cases, where that pointer may be useful.
  • @BenLee, I'm not IgorPopov ;-) And being not the OP, I already said that I find the pointer useful and your answer too, it is the "you should really be using" part that I dislike.
  • You omit a hasOwnProperty() test and things kinda keep working. Until they stop, because your objects became more complex over time. Except then it breaks mysteriously in an unrelated part of the code because too much was copied. And you don't have any context for debugging. JS sucks like that, so careful coding to prevent such problems from occurring is prudent.
  • I think this answer needs to be updated as per the following link developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… const target = { a: 1, b: 2 }; const source = { b: 4, c: 5 }; const returnedTarget = Object.assign(target, source); console.log(target); // expected output: Object { a: 1, b: 4, c: 5 } console.log(returnedTarget); // expected output: Object { a: 1, b: 4, c: 5 }
  • +1, another cool ES6 feature. Of course browser/even Node.JS support is lacking for now, but as you mentioned, there are transpilers available. And if you don't like them - shims: github.com/paulmillr/es6-shim (or standalone, Object.assign()-only shim: github.com/ljharb/object.assign ).