javascript - Copy object with results of getters - Stack Overflow

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I have an object that contains a getter.

myObject {
    id: "MyId",
    get title () { return myRepository.title; }
}

myRepository.title = "MyTitle";

I want to obtain an object like:

myResult = {
    id: "MyId", 
    title: "MyTitle"
}

I don't want to copy the getter, so:

myResult.title;                       // Returns "MyTitle"
myRepository.title = "Another title";
myResult.title;                       // Should still return "MyTitle"

I've try:

• $.extend(): But it doesn't iterate over getters.
• Iterating properties as suggested here, but it doesn't iterate over getters.
• As I'm using angular, using Angular.forEach, as suggested here. But I only get properties and not getters.

Any idea? Thx!

Update I was setting the getter using Object.defineProperty as:

 "title": { get: function () { return myRepository.title; }},

As can be read in the doc:

enumerable true if and only if this property shows up during enumeration of the properties on the corresponding object. Defaults to false.

Setting enumerable: true fix the problem.

"title": { get: function () { return myRepository.title; }, enumerable: true },

I have an object that contains a getter.

myObject {
    id: "MyId",
    get title () { return myRepository.title; }
}

myRepository.title = "MyTitle";

I want to obtain an object like:

myResult = {
    id: "MyId", 
    title: "MyTitle"
}

I don't want to copy the getter, so:

myResult.title;                       // Returns "MyTitle"
myRepository.title = "Another title";
myResult.title;                       // Should still return "MyTitle"

I've try:

• $.extend(): But it doesn't iterate over getters. http://bugs.jquery./ticket/6145
• Iterating properties as suggested here, but it doesn't iterate over getters.
• As I'm using angular, using Angular.forEach, as suggested here. But I only get properties and not getters.

Any idea? Thx!

Update I was setting the getter using Object.defineProperty as:

 "title": { get: function () { return myRepository.title; }},

As can be read in the doc:

enumerable true if and only if this property shows up during enumeration of the properties on the corresponding object. Defaults to false.

Setting enumerable: true fix the problem.

"title": { get: function () { return myRepository.title; }, enumerable: true },

• javascript
• getter-setter

Share Improve this question Follow edited May 23, 2017 at 12:15 CommunityBot 111 silver badge asked Nov 11, 2014 at 11:13 Mario LevreroMario Levrero 3,37744 gold badges2727 silver badges5959 bronze badges 3

• 3 Sorry, but your object is a syntax error. You need to remove :function after a get keyword; and you cannot have a normal title property and a getter with the same name. – Bergi Commented Nov 11, 2014 at 11:19
• 2 $.extend does work very well. The bug description says "jQuery.extend copies property getter return values, not their code." - however, that's just what you want. Doing it manually with for in will do the same. – Bergi Commented Nov 11, 2014 at 11:21
• Sorry @Bergi, the object sintax is just a copy of the console.log for the object. I'm going to update the question. – Mario Levrero Commented Nov 11, 2014 at 11:23

Add a ment  | 

3 Answers 3

Sorted by: Reset to default 4

$.extend does exactly what you want. (Update: You've since said you want non-enumerable properties as well, so it doesn't do what you want; see the second part of this answer below, but I'll leave the first bit for others.) The bug isn't saying that the resulting object won't have a title property, it's saying that the resulting object's title property won't be a getter, which is perfect for what you said you wanted.

Example with correct getter syntax:

// The myRepository object
const myRepository = { title: "MyTitle" };

// The object with a getter
const myObject = {
    id: "MyId",
    get title() { return myRepository.title; }
};

// The copy with a plain property
const copy = $.extend({}, myObject);

// View the copy (although actually, the result would look
// the same either way)
console.log(JSON.stringify(copy));

// Prove that the copy's `title` really is just a plain property:
console.log("Before: copy.title = " + copy.title);
copy.title = "foo";
console.log("After:  copy.title = " + copy.title);

<script src="https://ajax.googleapis./ajax/libs/jquery/1.11.1/jquery.min.js"></script>

Syntax fixes:

• Added missing variable declarations, =, and ;

• Removed duplicate property title

• Corrected the getter declaration syntax

---

If you want to include non-enumerable properties, you'll need to use Object.getOwnPropertyNames because they won't show up in a for-in loop, Object.keys, or $.extend (whether or not they're "getter" or normal properties):

// The myRepository object
const myRepository = { title: "MyTitle" };

// The object with a getter
const myObject = {
    id: "MyId",
};
Object.defineProperty(myObject, "title", {
    enumerable: false, // it's the default, this is just for emphasis,
    get: function () {
        return myRepository.title;
    },
});

console.log("$.extend won't visit non-enumerable properties, so we only get id here:");
console.log(JSON.stringify($.extend({}, myObject)));

// Copy it
const copy = {};
for (const name of Object.getOwnPropertyNames(myObject)) {
    copy[name] = myObject[name];
}

// View the copy (although actually, the result would look
// the same either way)
console.log("Our copy operation with Object.getOwnPropertyNames does, though:");
console.log(JSON.stringify(copy));

// Prove that the copy's `title` really is just a plain property:
console.log("Before: copy.title = " + copy.title);
copy.title = "foo";
console.log("After:  copy.title = " + copy.title);

.as-console-wrapper {
    max-height: 100% !important;
}

<script src="https://ajax.googleapis./ajax/libs/jquery/1.11.1/jquery.min.js"></script>

First of all, fix your syntax, though it probably is good in your actual code:

myObject = {
    id: "MyId",
    get title () { return myRepository.title; }
}

Now, to the answer. :)

You can just use a for..in loop to get all the properties, then save them as-is:

var newObj = {};
for (var i in myObject) {
    newObj[i] = myObject[i];
}

No jQuery, Angular, any other plugins needed!

I had the same issue but in TypeScript and the method mentioned by T.J. Crowder didnt work.

What did work was the following:

TypeScript:

function copyObjectIncludingGettersResult(originalObj: any) {

    //get the properties
    let copyObj = Object.getOwnPropertyNames(originalObj).reduce(function (result: any, name: any) {
        result[name] = (originalObj as any)[name];
        return result;
    }, {});

    //get the getters values
    let prototype = Object.getPrototypeOf(originalObj);
    copyObj = Object.getOwnPropertyNames(prototype).reduce(function (result: any, name: any) {
        //ignore functions which are not getters
        let descriptor = Object.getOwnPropertyDescriptor(prototype, name);
        if (descriptor?.writable == null) {
            result[name] = (originalObj as any)[name];
        }
        return result;
    }, copyObj);

    return copyObj;
}

Javascript version:

function copyObjectIncludingGettersResult(originalObj) {
  
    //get the properties
    let copyObj = Object.getOwnPropertyNames(originalObj).reduce(function (result, name) {
       
         result[name] = originalObj[name];
        
        return result;
    }, {});

    //get the getters values
    let prototype = Object.getPrototypeOf(originalObj);
     copyObj = Object.getOwnPropertyNames(prototype).reduce(function (result,name) {
let descriptor = Object.getOwnPropertyDescriptor(prototype, name);
        if (descriptor?.writable == null) {
            result[name] = originalObj[name];
        }
        return result;
    }, copyObj);
       
    return copyObj;
}

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