roslibjs example

foo.js

//* The Ros object, wrapping a web socket connection to rosbridge.
var ros = new ROSLIB.Ros({
  url: 'ws://localhost:9090' // url to your rosbridge server
});

//* A topic for messaging.
var exampleTopic = new ROSLIB.Topic({
  ros: ros,
  name: '/com/endpoint/example', // use a sensible namespace
  messageType: 'std_msgs/String'
});

/**
 * Serializes an object and publishes it to a std_msgs/String topic.
 * @param {ROSLIB.Topic} topic
 *       A topic to publish to. Must use messageType: std_msgs/String
 * @param {Object} obj
 *       Any object that can be serialized with JSON.stringify
 */
function publishEncoded(topic, obj) {
  var msg = new ROSLIB.Message({
    data: JSON.stringify(obj)
  });
  topic.publish(msg);
}

/**
 * Decodes an object from a std_msgs/String message.
 * @param {Object} msg
 *       Message from a std_msgs/String topic.
 * @return {Object}
 *       Decoded object from the message.
 */
function decodeMessage(msg) {
  return JSON.parse(msg.data);
}

/**
 * Typed messaging wrapper for a std_msgs/String ROS Topic.
 * @param {ROSLIB.Topic} topic
 *       A std_msgs/String ROS Topic for multiplexed messaging.
 * @constructor
 */
function RosTypedMessaging(topic) {
  this.topic = topic;
  this.topic.subscribe(this.handleMessage_.bind(this));
}
RosTypedMessaging.prototype.__proto__ = EventEmitter2.prototype;
 
/**
 * Handles an incoming message from the topic by firing an event.
 * @param {Object} msg
 * @private
 */
RosTypedMessaging.prototype.handleMessage_ = function(msg) {
  var decoded = decodeMessage(msg);
  var type = decoded.type;
  var data = decoded.data;
  this.emit(type, data);
};
 
/**
 * Sends a typed message to the topic.
 * @param {String} type
 * @param {Object} data
 */
RosTypedMessaging.prototype.sendMessage = function(type, data) {
  var msg = {type: type, data: data};
  publishEncoded(this.topic, msg);
};
 
//* Example implementation of RosTypedMessaging.
var myMessageChannel = new RosTypedMessaging(exampleTopic);
 
myMessageChannel.on('fooo', function(data) {
  console.log('fooo!', data);
});
 
setInterval(function() {
  var mySyncObject = {
    time: Date.now(),
    myFavoriteColor: 'red'
  };
  myMessageChannel.sendMessage('fooo', mySyncObject);
}, 1000);

how to receive and parse a custom message?

I think roslibjs (and most other things through rosbridge) don't need any extra help for custom messages. Just define messageType: 'my_pkg/MessageTypeName' and see if you can subscribe, and print out the message.