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Functional style in JavaScript

By Prabhu Sunderaraman on November 21, 2013 in

Here’s an example to convert the following imperative style of coding in JavaScript to functional style. The code prints out a list of even numbers in an array. 

var imperativeStyle = function(){
 var numbers = [1,2,3,4,5,6,7,8,9,10];
 var evenNumbers = [];
 for(var i=0;i<numbers.length;i++){
  if(numbers[i] % 2 == 0)
    evenNumbers.push(numbers[i]);
 }	
 console.log(evenNumbers);
};

The functional approach can be implemented using the filter() method of the Array class in JavaScript like this. 

var functionalStyle = function(){
 var numbers = [1,2,3,4,5,6,7,8,9,10];
 var evenNumbers = numbers.filter(function(num){
    return num % 2 == 0});
 console.log(evenNumbers);
};
functionalStyle();

The filter() function is a higher-order function that applies the function argument to all the elements in an array and returns a new collection.

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Swipe event in a Panel- Sencha Touch

By Prabhu Sunderaraman on November 10, 2013 in ,

Handling the pinch, touch and swipe events in components like Panel in Sencha Touch is a piece of cake. You have to register these events on the DOM element of the UI Component.

The UI Components in Sencha Touch have an element property (unfortunately the API documentation doesn’t show this;I am looking at touch 2.3.0) using which you can access the underlying HTML element. Here’s the code to register the swipe event on a Panel. 

  function panelSwiped(e) {
    console.log("Panel swiped: " + e.direction);
  }
  Ext.application({
    launch: function () {
      Ext.Viewport.add({
        xtype: "panel",
        listeners: {
           activate: function (src) {
                  src.element.on("swipe", panelSwiped);
           }
        },
        items: [
          { xtype: "titlebar", title: "Events" }
        ]
      });
   }
});
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What about Security? :)

By Prabhu Sunderaraman on November 3, 2013 in

Over the years developers have asked me several questions. The questions range from being seriously stupid to seriously smart ones. However there’re some questions which bowl me down often, no matter how many times I face them. Here’s a list of such questions.

  • What about Security? There’re are only two kinds of people who ask this question. People who are genuinely concerned about securing their applications or code and those who ask this question because they want to ask something. Unfortunately the former is a microscopic community. Once I got ticked off and told a developer that this question is like asking “What did you have for breakfast last year?”. I don’t know if he understood the point, but he seemed to be so amused :(
  • Can you show us the best practices? I would have been spending time writing thousands of lines of code discussing various features and scenarios, before I get this question. I try to say that I wouldn’t be writing horrible code and showing it to you and most of the code I write is a good(atleast not bad) quality production code. No, the guys don’t seem to be happy with the answer. They want me to give them a laundry list of best practices starting from how to write a best “Hello World” code.
  • Have you worked on complex projects? Complexity is a relative term. What is so complex to one may be a piece of cake for another. In fact, I have not come across anybody so far, who says he is working on a silly and simple project. Everybody takes so much pride in saying that theirs’ is a complex project even if it involves just taking some data and storing it in a database. I’m still working on a best answer for this question.
  • Does anybody in the industry use this?I usually want to scream NO, YOU’RE THE ONLY UNFORTUNATE SOUL IN THIS WORLD WORKING ON THIS. An “Yes” to this question always leads to a set of “Who are they?” questions. A “No” leads to a sorry face.
  • Can you cover some advanced topics in this training? It so happens that the guys who ask these questions are usually the ones who really don’t even know the basics. Several years ago I had to let go off an assignment because what the client considered an advanced topic was very basic to me and what I considered as advanced was supposedly very elementary to him.

As I type this article my Gmail pops with a new email notification from a client and the subject says “A couple of questions”. :) :(

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Getting started with MongoDB-IV

By Prabhu Sunderaraman on October 30, 2013 in ,

In the previous post, we discussed the CRUD operations in MongoDB. It’s time to get your hands dirty by writing some code. Let’s connect to MongoDB from Java, access our Quiz document and play with the Questions collection.

  • You need to download the MongoDB driver for Java here and add it to the classpath.
  • Start your mongodb server from command prompt.
  • You can connect to the MongoDB server, get a reference to the Quiz document and the Questions collection as shown here;

    DBAddress dbAddress = new DBAddress("localhost");
Mongo mongo = new Mongo(dbAddress);
DB quiz = mongo.getDB("Quiz");
DBCollection questions = quiz.getCollection("Questions");
  • Let’s insert a record in Questions collections as shown here. You don’t have to supply a JSON formatted data. You can create an instance of BasicDBObject and push it. The data will get serialized to JSON and be inserted into the document.

    BasicDBObject record = new BasicDBObject();
record.append("question", "10*9=?");
record.append("choices",new String[]{"19","1","90","100"});
record.append("answer", "90");
questions.insert(record);
  • Let’s fetch the data from the Questions collection. You can supply the query as a BasicDBObject instance and execute the records. You’ll get a DBCursor object that’s pretty similar to the ResultSet instance in JDBC.

    BasicDBObject query = new BasicDBObject();
query.append("question","10*9=?");
DBCursor dbCursor = questions.find(query);
while(dbCursor.hasNext()){
  BasicDBObject record = (BasicDBObject)dbCursor.next();
  System.out.println(record);
}

The Java class with the complete code is shown here.

import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBAddress;
import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.Mongo;

public class QuestionsClient {
  public static void main(String[] args) throws Exception{
    DBAddress dbAddress = new DBAddress("localhost");
    Mongo mongo = new Mongo(dbAddress);
    DB quiz = mongo.getDB("Quiz");
    DBCollection questions = quiz.getCollection("Questions");
		
    //INSERT A QUESTION
    BasicDBObject record = new BasicDBObject();
    record.append("question", "10*9=?");
    record.append("choices",new String[]{"19","1","90","100"});
    record.append("answer", "90");
    questions.insert(record);
		
    //LOAD
    BasicDBObject query = new BasicDBObject();
    query.append("question","10*9=?");
    DBCursor dbCursor = questions.find(query);
    while(dbCursor.hasNext()){
       BasicDBObject obj = (BasicDBObject)dbCursor.next();
       System.out.println(obj);
    }
 }
}

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Getting started with MongoDB-III

By Prabhu Sunderaraman on October 17, 2013 in ,

In the previous post we created a document called Quiz and inserted Questions into it. Each item in the Questions collection has a question, choices and answer. In this post let’s play with the CRUD operations. You can switch to Quiz document with “use Quiz” command.

  • You can retrieve questions using find() method. The find() method accepts two JSON objects as arguments. The first one is the criteria and the second is the filter. Let’s select the question and choices of all the questions whose answer is 5.
    db.Questions.find({answer:”5″},{question:1,choices:1,_id:0})

    The 1 and 0 in the second argument specify whether the field has to be retrieved or not. You will get an output as like this.

    blog1

  • Say you want to find the questions with answer as 2 and add “None of the above” option to the choices of questions. You can use the update() method for this purpose.

    db.Quiz.update({answer:”2″},{$push:{choices:”None of the above”}},{multi:true});
    The code above can be read as get all the items with answer as 2 and push “None of the above” to the choices property.
    blog2

  • If you want to delete a record you can use the remove() method.
    db.Questions.remove({answer:”5″});
    So, here we remove the records that have 5 as the answer.
    blog3

In the next post, let’s play with some more operations on the Questions data.

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