JavaScript : Selecting Elements in The DOM getElementById, getElementByTagName, getElementByClassName, querySelector, and querySelectorAll

In JavaScript the DOM is an acronym for "Document Object Model" that's quite a mouthful.  Most people just refer to it as the DOM.  The DOM is basically a collection of objects/elements organized in the tree structure.  To perform any functions in JavaScript you first have to find a reference to the object or element you are working with.  Luckily, there are a few handy JavaScript methods that can help you find the elements in the DOM that you want.

Let's take a look at the methods:

• getElementById - this method gets the element based on the unique id that is assigned to the                                   element
• getElementByClassName - this method gets the elements that has the class name that is passed                               into the method
• getElementByTagName - this method gets the elements that matches the tag name
• querySelector - this method gets the first child element that matches the CSS selector being                                passed in
• querySelectorAll - this method gets all the child elements that match the CSS selector

JavaScript : The switch Statement

The switch statement is there to make the code more readable if the if statements contains too many branches and becomes too hard to read.

Consider the code below

var x = 6;

if (x === 1)
{
     console.log("one");
}
else if (x === 2)
{
     console.log("two");
}
else if (x === 3)
{
     console.log("three");
}
else if (x === 4)
{
     console.log("four");
}
else if (x === 5)
{
     console.log("five");
}
else
{
     console.log("x is not 1-5");
}

JavaScript Basics: The for loop

The for loop is a looping construct in JavaScript that are more simplistic than the while loop.   When writing the for loop there are three three parts they are

1.  Initialize - a count variable is initialize, it's usually zero but it doesn't have to be
2. Test - A test to see if the loop should continue
3. Increment - finally the count is incremented, it doesn't have to be an increment it could be decrements as well

JavaScript : The ? Ternary Operator

The conditional ?: operator in JavaScript has three operands the first part goes before ? the second goes between the ? and the : symbol and the third operand goes after the : symbol.  You can think of this operator as shorthand way of writing a an if statement.  The first operand evaluates to a boolean, if the first operand is true then evaluate the second operand else evaluate the third operand.

Let's say we want to want to see what the gender of the baby is and assign it a name, let's demonstrate it with code.

var gender = "girl";

var name = gender === "boy" ? "Julian" : "Julie";

console.log(name);

The code above assigns the variable gender to "girl" then it uses the conditional ?: to assign a value to the variable name if the gender is "boy" then assign the name "Julian" to name, else assign the name "Julie"

JavaScript : Error Handling With try/catch/finally

JavaScript error handling is a lot like other languages where you have the try/catch/finally  statement that you can used.  The basic premise is

try
{
     // try some codes here fingers crossed that nothing bad happens
}
catch(ex)
{
     // oops something bad happened, this is where it gets handled or I tell the user
}
finally
{
    // I don't care what happens I am going to execute and get paid
}

Here is the error handling in action:

JavaScript Objects Deep Dive : Creating Objects With Object Literals

The most common ways you see how objects are created in JavaScript is the object literal syntax.  The object literal syntax is the open { } with comma separated name: pair value lists.  The name: part is the name of the property.  The part after : is the property value which can hold a primitive value or another object.  It could even be a function.

Here is an example of an object literal:

var product = {
    name: "Chai",
    Category: "Tea",
    Country: "India",
    supplier: {
        name: "ACME Tea Of India",
        location : "New Delhi"
    },
    related: ["Earl Grey", "Green Tea", "Dark Tea", "White Tea"],
    display: function () {
        console.log(this);
    }
};

JavaScript : The eval() Function

The eval() function in JavaScript provides the power of dynamic evaluation, it evaluates a strings of JavaScript codes and returns a value.  If you use the eval on pair of string numbers it will be forgiving and give you the number if it can.  For example if you type int

eval("4+5")  the result will be 9 even though it's a string

JavaScript Objects Deep Dive : Creating Objects With The new Keyword

In the previous post we visited how to create an object with an object literal.  In this post we are going to create the same object using the new keyword.  When creating objects using the new keyword it is required that the it is followed by a function call.  The purpose of this function call is the needs a way to call to the constructor of the new object.  A constructor is used to create or initialize the created object.

Here is the code to rewrite our literal object using the new keyword:

var product = new Object();

product.name = "Chai";
product.category= "Tea";
product.country= "India";
product.supplier= {
    name: "ACME Tea Of India",
    location: "New Delhi"
};

product.related = new Array("Earl Grey", "Green Tea", "Dark Tea", "White Tea");
product.display = function () {
    console.log(this);
};

JavaScript Objects Deep Dive : Create Objects With Object.Create

Object.Create( ) is a static function which can take two arguments.  The first argument is the prototype of the object, while the second argument is the properties of the argument.  A prototype is a second object that is created with every JavaScript object.  It is like a blueprint, or the model that the object is built on.  Think of it as a car prototype.

So let's create an object with Object.Create( ) function:

var person = Object.create({
    name: "Tech Junkie",
    location: "Mars",
    hobbie: "Video Games"
});

console.log(person);

JavaScript Objects Deep Dive : Flexibility of Array Notation

In JavaScript there are two ways to access an object, first by dot notation like this

product.name

or with array notation

product["name"]

They both get the job done.   However with the array syntax [""] you access the object as if it's an array but instead of accessing it by numbers or index you access it by the property names.  That's because JavaScript objects are associative arrays.  They look like other objects in other languages such as C, C++, and Java.  However they behave very differently.

In other languages objects are defined in advance, their properties are methods are fixed.  To add a property or method to the object you have to change the class the object instance is created from.

JavaScript Basics : The while loop

The while loop statement in JavaScript simply executes a statement block until a condition is not true anymore the syntax for the while loop is as follow

while (expression is true)
{
     execute these statements
}

The while loop is an iterative loop if the condition is true and the statements are executed, it starts at the top of the loop again and executes until the expression is false.  Therefore, there's a potential for an infinite loop.

JavaScript Basics : do/while Loop

The do/while loop is similar to the while loop.  The difference is that the first the loop expression is tested after the do statement block is executed at least once.  For example let's use our countdown example again.

If we have the code below the countdown displays the same results as the output.  However, the first iteration is performed without a evaluation of the expression.  It's not until the countdown is 9 that the while part of the loop kicks in.

JavaScript Basics : The for/in Loop

The for/in loop is a for loop that is used to iterate through the variables in an object. It can iterate to through that anything that can evaluated on the left side of the assignment expression call the LValues.  Let's use the for/in loop to iterate through an object "person".

Here we created an object called "person" with three properties we are going to use the for/in loop to display the property names as well as the values of those properties

var person = new Object();

person.name = "Tech Junkie";
person.occupation = "Blogger";
person.location = "Mars";

for(var p in person)
console.log(p + ": " + person[p]);

Python: Install Python On Linux

 The first thing you want to do in Python is to install the latest version of Python.  Even though most Linux and MAC distribution has Python installed by default, you still want to install the latest version of Python.  The latest stable version of Python at the time of this writing is version 3.8.5 in this post we are going to install version 3.6.5 on our Linux instance.  

1. Open up the terminal and type the following commands

sudo su

mkdir /opt/python

cd /opt/python/

wget https://www.python.org/ftp/python/3.8.5/Python-3.8.5.tgz

tar xzf Python-3.8.5.tgz

Python: Installing Python

In this post I am going to go over how to install Python on a Windows machine

Here are the steps to install Python

1.  Type in the URL https://www.python.org/downloads/
2.  Click Download Pythong 3.6.5, save it to a location that you will remember

C#: System.Collections.Generic.Dictionary

Namespace:

System.Collections.Generic

Declaration:

Dictionary<string, string> account = new Dictionary<string, string>();

Adding Items:

account.Add("id","1");
account.Add("username", "jackd");

Use in ArrayList: Namespace:

C# : Automatically Implemented Properties

There are times when you see a class property without it's private member counterpart and all you see is the {set; get;} accessors. What you are looking at are auto properties that you can create  in C#, the only requirements is that the set; and get; accessors contains no logic.  Usually there are private members that the properties expose to other classes using the get/set accessors, like the code below:

    public class Product
    {
        private int productId;
        private string name;
        private string description;
        private decimal price;

        public int ProductId
        {
            get
            { return productId; }
            set
            {
                productId = value;
            }
        }

        public string Name
        {
            get
            { return name; }
            set
            {
                name = value;
            }
        }

        public string Description
        {
            get
            { return description; }
            set
            {
                description = value;
            }
        }

        public decimal Price
        {
            get
            { return price; }
            set
            {
                price = value;
            }
        }

    }

C# : Arrays

Arrays are fixed size elements of a type, arrays are stored next to each other in the memory. Making them very fast and efficient.  However you must know the exact size of an array when you declare an array.

Declaring an array:

string[] names = new string[5];

There are two ways you can assign values to an array. The first is to assign the values individually by specify the index of the array inside a square bracket. The index is the position of element in the array. Index starts with 0.

names[0] = "George";
names[1] = "James";
names[2] = "Arthur";
names[3] = "Eric";
names[4] = "Jennifer";