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Do You Know JavaScript? Are You Sure? – Part 1

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28 Feb 2017CPOL6 min read
Some basics of JavaScript which you may have forgotten or you may not be aware of

Here, we are going to a series of articles related to JavaScript. As this is the first part of the series, here we are going to see some basics of JavaScript which you may have forgotten or you may not be aware of. You can always see my other posts related to JavaScript here. We will be using Visual Studio for our development. I hope you will like this. Now let’s begin.

Introduction

Basically, JavaScript is a programming language of HTML and Web. Now a days, we can create any kind of application using JavaScript. If you are totally new to JavaScript, I strongly recommend you read some basics here.

Background

Recently, I was assigned to a training task where I needed to train one of my colleagues who is a fresher and totally new to the programming field. I had covered almost all the topics in my training and I am sharing few of them here. I hope you will like this.

Create an HTML Page

As we already said, JavaScript is a programming language of HTML and Web, we need a page to work with JavaScript. Let’s create it first.

HTML
<!DOCTYPE html>
<html>
<head>
    <title></title>
	<meta charset="utf-8" />
</head>
<body>
</body>
</html>

Now, create a JS file and include it in your page.

JavaScript
<script src="JavaScript.js"></script>

Let’s Begin Our Tutorial

Any idea, what will be the output of the preceding lines of code.

JavaScript
console.log(2 + 2);
console.log(2 + "2");
console.log(2 + "2" + 2);
console.log(2 + 2 + "2" + 2);
console.log(2 + 2 + "2" + 2 + 2);
console.log(2 + "2" + 2 + "2" + 2 + 2);
console.log("2" + 2 + "2" + 2 + 2 + 2 + 2);

Once after you run your application, press CTRL+SHIFT+J if you are opening your application in Google chrome or CTRL+SHIFT+K if it is Mozilla, or press F12 if in Internet Explorer. This will open the browser console. Now check the output, is it the same as you thought?

Javascript_tutorial_output_1

Javascript_tutorial_output_1

If you noticed properly, console.log(2 + 2 + “2” + 2 + 2); returned 4222. First twos are added and when it comes to the third digit, the type of the result is being changed to string, so the string concatenation is happening. This is because of the dynamic nature of JavaScript.

So you can always add different types of values to the same variable in JavaScript. The preceding codes will always be working perfectly.

JavaScript
var a = 1;
a= = "Sibeesh";

Now a simple test, what will be the output of the preceding code?

JavaScript
var b;
console.log(b);

Yes, you are right, it will return undefined as we have not assigned any values to the variable b. Have you ever checked the typeof an undefined variable?

JavaScript
console.log(typeof(b));

The result will be undefined. Now what about the preceding codes?

JavaScript
console.log(typeof(undefined));
console.log(typeof(typeof(b))); 
console.log(typeof(String(b)));
console.log(typeof({a:b}));
console.log(typeof(null));

It can give you an output as below:

JavaScript
undefined
string
string
object
object

Here one thing to be noted is, typeof(typeof()) will always return string. And {a:b}, null is actually objects so the typeof will return the type as object. Let’s write a simple program now.

JavaScript
var a=1;
var b=a;
a=2;

console.log(b);
console.log(a);

See, how simple it was. Any idea what would be the output of that? If your answer is 1 & 2, then you are right? Have you ever thought why that is so? This is because the variable we just created are primitive types. In primitive data types, the values are saved directly on the variable. If you are coming from the backgound of C#, you can understand the value typed variable.

Now we have one more data type which is referenced variable where values are stored as a reference not as direct values. An example for a referenced type variable is Object. Let’s go on to the next topic which is an overview on JavaScript Objects. Do you know how to create an object?

JavaScript
var myName = {firstName: "Sibeesh", lastName: "Venu"};
console.log(myName);
console.log(JSON.stringify(myName));
console.log(myName.firstName);
console.log(myName.lastName);

Here, myName is an object. You can always use JSON.stringify() to make your object to a string format and JSON.parse() to make your string to object. So, the above code will give you an output as follows:

Javascript_tutorial_output_2

Javascript_tutorial_output_2

An object is a collection of key-value pairs, like we see in the above object, firstName is key and “Sibeesh” is value. How can we take any values from an object? We can always access a property from an object using dot(.) operator as follows:

JavaScript
console.log(myName.firstName);
console.log(myName.lastName);

The above code will give you an output as “Sibeesh” “Venu”, right? We just access a property from an object. Now we have given string value to our object as a key? Is there anyway we can give a key in number format? Let’s have a look.

JavaScript
var myName = {1: "Sibeesh", 2: "Venu"};

The question is, how can we access values of the keys 1 & 2? Like below?

JavaScript
console.log(myName.1);
console.log(myName.2);

If you said “Yes”, you are wrong. If you try to access the values as above. This will throw an “Uncaught SyntaxError” error, so how can we access it?

JavaScript
console.log(myName["1"]);
console.log(myName["2"]);

So when the key value is a number, we must use [] for accessing the values. Now let's go back to the previous object.

JavaScript
var myName = {firstName: "Sibeesh", lastName: "Venu"};
var myNameCopy= myName;
myName.firstName = "Sibi";

console.log(myName.firstName);
console.log(myNameCopy.firstName);

Any idea what will be the output of the above code? Have you just said Sibi Sibeesh? Oh, man. You got confused. The actual output is Sibi Sibi. As we said earlier, an object is an example of referenced type variable where the values are stored as a reference to it. So even if we change the value of our first object, that will reflect in our second one too.

In the above examples, we have created objects like below:

JavaScript
var myName = {firstName: "Sibeesh", lastName: "Venu"};

This way of careating an object is called Object literals. Now the question is, is this the only way of creating the object? There is one more way, which is known as Object Constructor. Now we can create the same objects in Object constructor way.

JavaScript
var myName = new Object();
myName.firstName = "Sibeesh"
myName.lastName = "Venu";
console.log(myName.firstName);
console.log(myName.lastName);

Is there any rule that we can add only variables to an object? Absolutely no, an object can hold a function too. Let’s create an object with a function inside.

JavaScript
var myName = {
firstName: "Sibeesh", 
lastName: "Venu",
myFullName: function(){
console.log(myName.firstName+" "+myName.lastName);
}
};

So the code myName.myFullName(); will return my full name “Sibeesh Venu” as output. Right? So from the above code, we can create a functions in JavaScript as follows?

JavaScript
var myFullName =  function(firstName, lastName){
return firstName + " " + lastName;
}

If you call the above function as preceding, you will get an output as “Sibeesh Venu”:

JavaScript
console.log(myFullName("Sibeesh","Venu"));

The question is, what if we are passing only one value? Let’s try that out.

JavaScript
console.log(myFullName("Sibeesh"));

If you are working in any server side languages, this will actually give an error like “function with one parameter couldn’t find”. But JavaScript is not like that, even if you are wrong, it will try to make you right. So in this case, it actually treats the second parameter as undefined and gives you an output as “Sibeesh undefined”.

That’s all for today. You can always download the source code attached to see the complete code and application. Happy coding!.

References

See Also

Conclusion

Did I miss anything that you may think is needed? Could you find this post useful? I hope you liked this article. Please share your valuable suggestions and feedback.

Your Turn. What Do You Think?

A blog isn't a blog without comments, but do try to stay on topic. If you have a question unrelated to this post, you're better off posting it on C# Corner, Code Project, Stack Overflow, ASP.NET Forum instead of commenting here. Tweet or email me a link to your question there and I'll definitely try to help if I can.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Sibeesh Passion
Software Developer
Germany Germany
I am Sibeesh Venu, an engineer by profession and writer by passion. I’m neither an expert nor a guru. I have been awarded Microsoft MVP 3 times, C# Corner MVP 5 times, DZone MVB. I always love to learn new technologies, and I strongly believe that the one who stops learning is old.

My Blog: Sibeesh Passion
My Website: Sibeesh Venu

Comments and Discussions

 
Questionvery nice illustration Pin
saransh892-Mar-17 17:07
professionalsaransh892-Mar-17 17:07 
AnswerRe: very nice illustration Pin
Sibeesh Passion2-Mar-17 17:57
professionalSibeesh Passion2-Mar-17 17:57 
Questionincluding object keys Pin
borchef2-Mar-17 1:51
Memberborchef2-Mar-17 1:51 
AnswerRe: including object keys Pin
Sibeesh Passion2-Mar-17 17:58
professionalSibeesh Passion2-Mar-17 17:58 
Thanks much for the hint. I will definitely add it in my next part.
==================!!!====================!!!========================
So much complexity in software comes from trying to make one thing do two things.
Kindest Regards
Sibeesh Venu
http://sibeeshpassion.com/

QuestionMy vote of 5 Pin
Dupsi Yupsi28-Feb-17 21:25
MemberDupsi Yupsi28-Feb-17 21:25 
AnswerRe: My vote of 5 Pin
Sibeesh Passion28-Feb-17 22:30
professionalSibeesh Passion28-Feb-17 22:30 

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