refactoring,

added isAvailable function,
added examples

example.js

@@ -13,3 +13,10 @@ portchecker.getFirstAvailable(startPort, endPort, host, function(p, host) {
         console.log('the first free port found on ' + host + ' between ' + startPort + ' and ' + endPort + ' is ' + p);
     }
 });
+
+
+//---- check if the port is open ---------------------------------------------------
+
+//portchecker.isOpen(81, 'localhost', function(isOpen){
+//    console.log('port 81 on localhost is ' + (isOpen ? 'open' : 'closed'));
+//})

portchecker.js

@@ -14,28 +14,45 @@ var net = require('net');
 
 
 // start port, last port, host, callback
-exports.getFirstAvailable = function (p, m, host, callback) {
+exports.getFirstAvailable = function (startPort, endPort, host, callback) {
+    if (startPort>endPort) {
+        throw new Error('portchecker: startPort must be lower than endPort');
+    }
+    console.log('looking for an available port in ' + startPort + '-' + endPort + ' on ' + host);
     var notFree = false;
+    var currentPort = startPort;
+
+    var onCheckPort = function(isOpen){
+        isOpen && check();
+        !isOpen && callback((currentPort-1), host);
+    }
+
+    var check = function() {
+        //---- return -1 if we checked all ports from the range already
+        currentPort>endPort && callback(-1, host);
+
+        console.log('checking :' + currentPort);
+        exports.isOpen(currentPort, host, onCheckPort);
+        currentPort++;
+    }
+
+    //----- start checking ----------
+    check();
+
+
+}
+
+exports.isOpen = function (p, host, callback) {
+    var isOpen = false;
     var conn = net.createConnection(p, host);
     var onClose = function() {
-        if (notFree) {conn.connect(p); notFree = false; return;}
         delete conn;
-        callback(p, host);    
+        callback(isOpen);    
     };
 
     var onOpen = function() {
-        notFree = true;
+        isOpen = true;
         //console.log(host+":"+p+" is taken");
-
-        //not found
-        if (p >= m) { 
-            conn.removeListener('close', onClose);
-            delete conn;
-            callback(-1, host); 
-
-        }
-
-        p++;
         conn.end();
     };