final concurrency examples

futures/callbackhell.js

@@ -0,0 +1,14 @@
+fetch1(request1, function (response1) {
+    // phase 1
+    var request2 = step1(response1);
+
+    fetch2(request2, function (response2) {
+        // phase 2
+        var request3 = step2(response2);
+
+        fetch3(request3, function (response3) {
+            // phase 3
+            step3(response3);
+        });
+    });
+});