api.js

var chatServer = {
  /**
   * Invoke function. callback will be invoked with (err, list). error is any server error and list is JSON format
   * of some yet to be defined type that basically covers all your contact list rendering need
  **/
  getContacts: function (callback) { /* code you don't care about */ },
  /**
   * Callback will be invoked with (err, call)
   *
  **/
  voiceCall: function (userId, callback) { /* code you don't care about */ }
}

chatServer.on("incomingCall", function (call) { /* your code */ });

var Call = {
  acceptCall: function () { /* my code */ },
  endCall: function () { /* my code */ }
};