在Javascript中模拟子类 - 检查我是如何做到的？

Question

I'm writing some javascript that's GNOME javascript, which is more-or-less spidermonkey. Think of it as spidermonkey code that will never be run outside of spidermonkey, so no need to worry about cross-browser compatibility etc.

Basically I have a class Folks.Individual that is not subclassable, but I want to simulate subclassing it by just patching it, adding a few getters to it. (For those that are interested, it is a GObject obtained via gobject introspection and in my version of GJS you can't subclass a GObject ).

Notes:

• contactSys.get_individual(contactID) returns the Folks.Individual I'm patching
• I add some getters email , aliasText , and online that return some values.
• I use this class via let contact = new Contact(id); , and simply want to use contact as if it were a Folks.Individual , plus the extra properties I patch in.

• If the properties I wanted to patch were not dynamic, I'd just do it like so:

   let contact = contactSys.get_individual(contactID); contact.email = ....; contact.aliasText = ....; contact.online = ....; 

I simply want a convenience function about the above such that I can call let contact = new Contact(contactID) and it will return contact with the email , aliasText and online properties patched in (as getters though).

This is how I've done it at the moment. My question is, is this the "proper" way to do it? Should I be using this instead of contact within Contact() ? Should I be doing something with Folks.Individual.prototype instead and calling it a Contact ?

function Contact (contactID) {                                                  
    let contactSys = Shell.ContactSystem.get_default(),                         
        contact    = contactSys.get_individual(contactID); // <-- this is a Folks.Individual
    contact._contactSys = contactSys;                                           

    /* these are defined as getters in case the underlying values change */     
    Object.defineProperty(contact, 'email', {get: function () {                 
        return contact._contactSys.get_email_for_display(this);                 
    }});                                                                        
    Object.defineProperty(contact, 'aliasText', {get: function () {             
        return contact.alias     ||                                             
               contact.full_name ||                                             
               contact.nickname  ||                                             
               contact.email     ||                                             
               _("Unknown");                                                    
    }});                                                                        
    Object.defineProperty(contact, 'online', {get: function () {                
        return contact.presence_type === Folks.PresenceType.AVAILABLE ||        
               contact.presence_type === Folks.PresenceType.AWAY ||             
               contact.presence_type === Folks.PresenceType.EXTENDED_AWAY ||    
               contact.presence_type === Folks.PresenceType.BUSY;               
    }});                                                                        
    return contact;                                                             
}                 

Remember - I can't subclass Folks.Individual , so I'll settle for patching instances of it with a wrapper function new Contact(contactID) so that I can treat it as if it were a subclass. I just want to know if there's a standard way of doing this.

cheers!

Answer 1

At the very least you can probably do 'online' a bit more succinctly and efficiently:

var ONLINE = Folks.PresenceType.AVAILABLE |
              Folks.PresenceType.AWAY |
              Folks.PresenceType.EXTENDED_AWAY |
              Folks.PresenceType.BUSY;

Object.defineProperty(contact, 'online', {
  get: function(){ return (this.presence_type & ONLINE) > 0 }
});