Update beginners-guide.md

docs/docs/beginners-guide.md

@@ -4,3 +4,62 @@ title: Beginner's Guide
 ---
 
 [beginners-guide](unfinished-article)
+
+proper implementation of bluebird will help you chain your function synchronously.
+
+Example 1 :
+
+Code :
+
+    var express = require('express');
+    var fs = require('fs');
+    var app = express();
+
+
+    app.get('/index', function(req,res){
+    var index =fs.readFile('./views/index.html', 'utf8') //Async function
+    res.send(index)
+    });
+    var port = process.env.PORT || 3000
+    app.listen(port, function () {
+        console.log("Server is running at:" + port)
+    })
+
+In above code, it is suppose to fetch the index.html file and then send the response. But when you run it, it will not return you anything but an empty page.
+Reason : fs.readFile is an async methods, so even before read operation is completed action is passed to next command which is res.send.
+         So empty response is sent.
+
+## Solution with bluebird
+
+code :
+
+      var express = require('express');
+      var promise = require('bluebird');
+      var fs = require('fs');
+      var app = express();
+      var index;
+      var getIndex = function(){ 
+         return new promise(function(resolve,reject){
+
+          fs.readFile('./views/index.html', 'utf8', function(err,data){
+          if(err){
+           reject(err);
+          }
+          else{
+            index=data;
+            resolve(index);
+          }
+              })
+          })
+      };
+
+      app.get('/index', function(req,res){
+          getIndex().then( function(){ //bluebird promise objects make sures that next command is executed only once promise is either                                            resolved or rejected.
+          res.send(index)
+          });
+      })
+
+      var port = process.env.PORT || 3000
+      app.listen(port, function () {
+          console.log("Server is running at:" + port)
+      })