gistfile1.cs

dictionary ContactFieldInitializer {
  sequence<DOMString>? type;
  DOMString?           value;
};

[Constructor(sequence<DOMString> type, DOMString value, boolean pref),
 JSImplementation="@mozilla.org/contactField;1"]
interface ContactField {
  attribute any         type;
  attribute DOMString?  value;

  object toJSON();
};

dictionary ContactProperties {
  sequence<ContactFieldInitializer>?      email;
};

[Constructor(optional ContactProperties properties),
 JSImplementation="@mozilla.org/contact;1"]
interface mozContact {
  attribute any                         email;

  object toJSON();
};

gistfile2.js

function Contact() { }

Contact.prototype = {
  init: function(aWindow) {
    this._window = aWindow;
  },

  __init: function(aProp) {
    if (aProp.email) {
      this.email = [];
      for (let email of aProp.email) {
        let obj = new this._window.ContactField(email.type, email.value, email.pref);
        this.email.push(obj);
      }
    } else {
      this.email = null;
    }
  },

  toJSON: function() {
    return {
      email: this.email
    };
  },

  classID: Components.ID("{72a5ee28-81d8-4af8-90b3-ae935396cc66}"),
  contractID: "@mozilla.org/contact;1",
  classDescription: "Contact",
  QueryInterface: XPCOMUtils.generateQI([Ci.nsIDOMGlobalPropertyInitializer, Ci.nsISupports])
};

gistfile3.js

function ContactManager() { }

ContactManager.prototype = {
  _convertContact: function(aContact) {
    return new this._window.mozContact(aContact, {id: aContact.id,
                                                  published: aContact.published,
                                                  updated: aContact.updated});
  },

  _convertContacts: function(aContacts) {
    let contacts = [];
    for (let i in aContacts) {
      contacts.push(this._convertContact(aContacts[i]));
    }
    return contacts;
  },

  receiveMessage: function(aMessage) {
    let msg = aMessage.json;

    switch (aMessage.name) {
      case "Contacts:Find:Return:OK":
        let req = this.getRequest(msg.requestID);
        if (req) {
          let result = this._convertContacts(msg.contacts);
          Services.DOMRequest.fireSuccess(req.request, result);
        }
        break;
    }
    this.removeRequest(msg.requestID);
  },

  save: function(aContact) {
    let reason;
    if (aContact.id === "undefined") {
      aContact.setMetadata(this._getRandomId().replace(/[{}-]/g, ""));
      reason = "create";
    } else {
      reason = "update";
    }

    let request = this.createRequest();
    let options = { contact: aContact, reason: reason };
    let allowCallback = function() {
      cpmm.sendAsyncMessage("Contact:Save", {requestID: this.getRequestId({request: request, reason: reason}), options: options});
    }.bind(this);
    this.askPermission(reason, request, allowCallback);
    return request;
  },

  classID: Components.ID("{1d70322b-f11b-4f19-9586-7bf291f212aa}"),
  contractID: "@mozilla.org/contactManager;1",
  classDescription: "ContactManager",
  QueryInterface: XPCOMUtils.generateQI([Ci.nsIDOMGlobalPropertyInitializer, Ci.nsISupports])
};

gistfile4.js

var c = new mozContact({email: {type: ["work"], value: "foo@bar"}});
navigator.mozContacts.save(c).onsuccess = function() {
  c.email = [{value: "foo"}];
  navigator.mozContacts.save(c); // boom! email is not a ContactField
};