Add example to demonstrate drain()

examples/drain.js

@@ -0,0 +1,45 @@
+var SerialPort = require("serialport").SerialPort;
+
+var sp = new SerialPort("/dev/cu.Cubelet-RGB", {
+    baudrate: 38400
+  });
+
+sp.on('open',function() {
+  sp.on('data', function(data) {
+    console.log('>>>>>', data);
+  });
+
+  var message = new Buffer('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa');
+
+  function writeThenDrainThenWait(duration) {
+    console.log('Calling write...');
+    sp.write(message, function() {
+      console.log('...Write callback returned...');
+      // At this point, data may still be buffered and not sent out from the port yet (write function returns asynchrounously).
+      console.log('...Calling drain...');
+      sp.drain(function() {
+        // Now data has "left the pipe" (tcdrain[1]/FlushFileBuffers[2] finished blocking).
+        // [1] http://linux.die.net/man/3/tcdrain
+        // [2] http://msdn.microsoft.com/en-us/library/windows/desktop/aa364439(v=vs.85).aspx
+        console.log('...Drain callback returned...');
+        console.log('...Waiting', duration, 'milliseconds...');
+        setInterval(writeThenDrainThenWait, duration);
+      });
+    });
+  };
+
+  function writeThenWait(duration) {
+    console.log('Calling write...');
+    sp.write(message, function() {
+      console.log('...Write callback returned...'); // Write function call immediately returned (asynchrounous).
+      console.log('...Waiting', duration, 'milliseconds...');
+      // Even though write returned, the data may still be in the pipe, and hasn't reached your robot yet.
+      setInterval(writeThenWait, duration);
+    });
+  };
+
+  // Stuff starts happening here
+  writeThenDrainThenWait();
+  //writeThenWait();
+
+});