openPorts.js

var openPorts = ( function() {
  var index = 0;
  var ports = {};
  var op = {
    getPorts: function() {
      var result = {};
      for(var id in ports){
        result[id] = ports[id];
      }
      return result;
    },
    getPortsArray: function() {
      var result = [];
      for(var id in ports){
        result.push(ports[id]);
      }
      return result;
    },
    get: function(id) {
      return ports[id];
    },
    add: function(port) {
      var id = index;

      ports[id] = port;
      port.onDisconnect.addListener(function() {
        op.remove(id);
      });

      index++;
      return id;
    },
    remove: function(id) {
      delete ports[id];
    },
    messageAll: function(message) {
      for(var id in ports){
        ports[id].postMessage(message);
      }
    }
  };
  return op;
})();

chrome.runtime.onConnect.addListener( function(port) { openPorts.add(port); } );

// ...

openPorts.messageAll({hello: "world"});