app.angular.js

'use strict';
// Declare app level module which depends on views, and components
angular.module('appName', [
    ...
    'appName.socket'
])

controller.angular.js

angular.module('appName.ctrlName', ['ngRoute'])
.controller('ctrlName', ['appName.socket',... ,
function(socket, ...) {
  socket.on('event', function(data){
        //play with data and scope
        $scope.varName = data.stuff;
    });
}]);

socketFactory.angular.js

angular.module('appName.socket',[])
.factory('appName.socket', function ($rootScope) {
    var host = "ip, localhost by default.";
    var port = 8080; //or whatever uou use.
    var socket = io.connect(host + ':' + port); //connect() will go to hostname by default
  return {
    on: function (eventName, callback) {
      socket.on(eventName, function () {
        var args = arguments;
        $rootScope.$apply(function () {
          callback.apply(socket, args);
        });
      });
    },
    emit: function (eventName, data, callback) {
        socket.emit(eventName, data, function () {
            var args = arguments;
            $rootScope.$apply(function () {
                if (callback) {
                    callback.apply(socket, args);
                }
            });
        });
    }
  };
});