How to write a javascript clone function that can copy added object methods?

Question

I have a javascript object cloning question. I'd like to be able to clone object methods that have been altered from those defined by the object prototype, or added to the object after instantiation. Is this possible?

The setting here is a javascript 'class' defined by me, so I'm fine with writing a clone method specific to my object class. I just can't figure out how to copy methods.

Example:

function myObject( name, att, dif ) {
    /* 'privileged' methods */
    this.attribute = function(newAtt) {  // just a getter-setter for the 'private' att member
        if(newAtt) { att = newAtt; }
        return att;
    }
    // 'public' members
    this.printName = name;
}

myObject.prototype.genericMethod = function() {
    // does what is usually needed for myObjects
}


/* Create an instance of myObject */
var object153 = new myObject( '153rd Object', 'ABC', 2 );
// object153 needs to vary from most instances of myObject:
object153.genericMethod = function() {
    // new code here specific to myObject instance object153
}
/* These instances become a collection of objects which I will use subsets of later. */


/* Now I need to clone a subset of myObjects, including object153 */
var copyOfObject153 = object153.clone();
// I want copyOfObject153 to have a genericMethod method, and I want it to be the one
// defined to be specific to object153 above.  How do I do that in my clone() method?
// The method really needs to still be called 'genericMethod', too.

Are you looking for a deep clone or is a shallow clone enough? — Ruan Mendes
– Ruan Mendes, Commented Sep 16, 2011 at 16:26
The requirement sounds really strange, what do you want to do with these clones, can you give an example? — Ruan Mendes
– Ruan Mendes, Commented Sep 16, 2011 at 16:36
I'm never quite certain what is meant by 'deep' vs. 'shallow' when cloning Javascript objects. My objects will not have any other objects as members, if that's what you mean, unless a method counts as an object. — bioJim
– bioJim, Commented Sep 16, 2011 at 18:45
The actual setting is for a helper application for gaming. The objects I describe above are character skills, which there are several hundred of in the game. Each has a set of characteristics, which can be defined similarly, but not identically. Some of these characteristics (the skill 'level', for instance - how good the character is at this skill) are derived, and therefore dynamic, so a method is required to calculate them - and many of the skills have unique versions of these. So I have a basic Skill object, with some prototype methods, which work for many of them but not all. — bioJim
– bioJim, Commented Sep 16, 2011 at 18:58
I am implementing this by instantiating a Skill object for each skill in the rules. Those requiring unique versions of methods like 'level' then have these defined and attached after instantiation. But then there will be a Character object, which will have cloned copies of some of these skills (when the character 'takes' those skills). To summarize, there will be a kind of canonical set of these Skill objects, similar to each other but distinct, and each Character will contain a (cloned) subset of these. — bioJim
– bioJim, Commented Sep 16, 2011 at 18:58

db48x · Accepted Answer · 2011-09-16 16:31:28Z

1

In your clone function, test each method on the object to see if it is equal to the same method on the object's constructor's prototype.

if (obj[method] != obj.constructor.prototype[method])
    clone[method] = obj[method];

answered Sep 16, 2011 at 16:31

db48x

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Ruan Mendes · Accepted Answer · 2011-09-16 19:12:25Z

0

It sounds like you just want a shallow copy. However beware of that objects are shared among instances since we're not deep copying.

function clone(obj) {
   var newObj = new obj.constructor();
   for (var prop in obj) {
     newObj[prop] = obj[prop];
   }
   return newObj;
}
var cloned = clone(object153);

A different syntax would be

myObj.prototype.clone = function() {
   var newObj = new this.constructor();
   for (var prop in this) {
     newObj[prop] = this[prop];
   }
   return newObj;
}
var cloned = object153.clone();

Try it out and see if it works for you, it's still hard to tell what you're doing. If it doesn't, explain why, then I can better understand the problem.

answered Sep 16, 2011 at 19:12

Ruan Mendes

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