How To Deep Copy (clone) An Object With Array Members In Javascript?

Introduction I have a Class Persons that contains an array of Person and functions : function Persons() { this.mItems = []; // Array of Objects Person } Persons.prototype = {

Solution 1:

If you're dealing with custom classes, you're going to want to implement custom clone methods. Generally, in this context, I'd have 2 separate clone functions, one on the Person model and one on the Persons collection.

Persons.prototype = {
  clone: function() {
    var clone = new Persons();
    clone.mItems = this.mItems.map(function(person) {
        return person.clone();
    });
    return clone;
  }
}

Person.prototype = {
  clone: function() {
    var clone = new Person(this.name);
    clone.score = this.score;
    return clone;
  }
}

The advantage to this approach is that it separates the concerns - the Person class doesn't have to know how to clone a single Person, it only has to know that Person exposes a clone method. If Person adds a new property that should be persisted in the clone, only Person needs to change.

It's generally an anti-pattern to use generic clone methods, e.g. from jQuery or Underscore, in this context. They'll end up cloning things you don't want, or missing things you do (e.g. a Person might eventually have an Address or some other object that will also need cloning).

Solution 2:

You can use [].map and Object.assign:

Persons.prototype.clone = function() {
   var clone = new Persons();
   clone.mItems = this.mItems.map(function(person) {
     return Object.assign(new Person, person);
   });
   return clone;
};