Add getLastMessage() for easier key/value storing.

static/cosmopolite.js

@@ -228,6 +228,21 @@ Cosmopolite.prototype.getMessages = function(subject) {
   return this.subscriptions_[subjectString].messages;
 };
 
+/**
+ * Fetch the most recent message for a subject
+ *
+ * @param {!string} subject Subject name
+ * @const
+ */
+Cosmopolite.prototype.getLastMessage = function(subject) {
+  var messages = this.getMessages(subject);
+  if (messages.length) {
+    return messages[messages.length - 1];
+  } else {
+    return null;
+  }
+};
+
 /**
  * Fetch all current pins for a subject
  *

static/test.js

@@ -240,7 +240,7 @@ test('getMessages/subscribe', function() {
 });
 
 asyncTest('subscribe barrier', function() {
-  expect(3);
+  expect(4);
 
   var subject = randstring();
   var message = randstring();
@@ -254,6 +254,7 @@ asyncTest('subscribe barrier', function() {
       equal(cosmo.getMessages(subject).length, 1, 'one message');
       equal(cosmo.getMessages(subject)[0]['subject']['name'], subject, 'subject matches');
       equal(cosmo.getMessages(subject)[0]['message'], message, 'message matches');
+      deepEqual(cosmo.getMessages(subject)[0], cosmo.getLastMessage(subject), 'getLastMessage works');
       cosmo.shutdown();
       start();
     });