Add isOpen() method

README.md

@@ -329,6 +329,10 @@ The `buffer` parameter accepts a [`Buffer` ](http://nodejs.org/api/buffer.html)
 
 Called once the write operation returns. The callback should be a function that looks like: `function (error) { ... }` _Note: The write operation is non-blocking. When it returns, data may still have not actually been written to the serial port. See `drain()`._
 
+### .isOpen()
+
+returns `true` if the port is open, otherwise false.
+
 ### .pause ()
 
 Pauses an open connection.

serialport.js

@@ -204,6 +204,12 @@ function SerialPortFactory() {
       if (callback) { callback(); }
     });
   };
+
+
+  SerialPort.prototype.isOpen = function() {
+    if (this.fd) return true;
+    else return false;
+  }
 
   SerialPort.prototype.write = function (buffer, callback) {
     var self = this;