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Posted 4 Mar 2017

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

, 4 Mar 2017
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More about JavaScript

Here, we are going to see another article of the JavaScript series. In the first part, we have seen some basics that you can start with. In this article, we will be discussing about the JavaScript object continuations and constructors, etc. You can always see my other posts related to JavaScript here. We will be using Visual Studio for our development. If you are totally new to JavaScript, I strongly recommend you to read some basics here. I hope you will like this. Now let’s begin.

Background

This article is the second part of the series we have just started. If you haven’t read the first part yet, I strongly recommend you read it here.

Setting Up the Platform

To get started with, here we are going to create an HTML file and JS file.

<!DOCTYPE html>
<html>
<head>
    <title>Do you know JavaScript? Are you sure? Part Two</title>
	<meta charset="utf-8" />
    <script src="JavaScript.js"></script>
</head>
<body>

</body>
</html>

Let’s Begin Our Tutorial

Now, please open your JavaScript file. We have some scripts to write.

Constructor

Have you ever created any constructor in JavaScript? Before going to create one, it is better to know what is the need for it. Let’s start with an example. Here, I am going to create an object called bike.

var bike = {
    name: "Thunderbird",
    color: "Blue",
    CC: "350",
    company: "Royal Enfield",
    tankCapacity: "20",
    abs: false,
    showName: function () {
        console.log(this.name);
    }
};

As you can read it, this object is holding the common properties of my bike Royal Enfield Thunderbird. Now my question is whether this is the only bike you know? Absolutely no, right? So suppose you need to create an object for the brand new Bajaj Dominor? What will you do? Create another object? So what if you know more than 10 bikes. If your answer is creating 10 objects, that’s not fair at all. Instead, why don’t we share the common properties like name, color, cc, etc. So we are going to create objects, but we are not going to create the properties again. So let’s create an object for Dominor. Before doing that, we need to create a bike constructor as follows:

function Bike(name, color, cc, company, tankCapacity, abs) {
    this.name = name;
    this.color = color;
    this.cc = cc;
    this.company = company;
    this.tankCapacity = tankCapacity;
    this.abs = abs;
    this.showName = function () {
        console.log('The name of the currnet bike is ' + this.name);
    }
}

Now, we can create object for Dominor as follows. Remember, when you write the word Bike, you can see that the intellisense is shown for you as follows:

Constructor_intellisence

Constructor_intellisence
var dominor = new Bike("Dominor", "Black", "Bajaj", "20", true);
dominor.showName();

Have you noticed that we have not created the function showName in the object dominor but in Bike, and we are still able to use that in the object dominor. And you can see an output as shown in your browser console.

Dominor_object_output

Dominor_object_output

And you can create an object for Royal Enfield Thunderbird as follows:

var thunderbird = new Bike("Thunderbird", "Marine", "Royal Enfield", "20", false);
thunderbird.showName();

Thunderbird_output

Thunderbird_output

Distinguish Between Own and Inherited Properties

As the heading implies, we have two kinds of properties, own and inherited. Let’s create an example to understand that.

var thunderbird = new Bike("Thunderbird", "Marine", "Royal Enfield", "20", false);
thunderbird.isMine = true;

console.log(dominor.name + " is yours or not? ");
console.log("isMine" in dominor);
console.log(thunderbird.name + " is yours or not? ");
console.log("isMine" in thunderbird);
console.log("toString" in dominor);
console.log("toString" in thunderbird);

Before running it, can you please guess what will be the output of the above code block? If you find the answer, check whether your answer matches the below output.

Own_and_inherited_properties

Own_and_inherited_properties

So isMine is the property that we just added to the object thunderbird, and the same is not available in the object dominor. That’s cool. But why is the property toString available in both objects, we have not added that to our object, right? This is because toString method is being inherited from the Object.prototype.

Use of hasOwnProperty

In the above code, we have just seen how to check if any property is available in our object, but that doesn’t mean it is its own property, right? To check that, we can use the hasOwnProperty. Let’s find out how to use it now.

console.log(dominor.name + " is yours or not? ");
console.log(dominor.hasOwnProperty("isMine"));
console.log(thunderbird.name + " is yours or not? ");
console.log(thunderbird.hasOwnProperty("isMine"));
console.log(dominor.hasOwnProperty("toString"));
console.log(thunderbird.hasOwnProperty("toString"));

Once again, please try to answer it on your own, before you run it.

hasOwnProperty_output

hasOwnProperty_output

Looping Through the Object

To loop through each item in an object, you can use for loop as follows:

for (var itm in thunderbird) {
    console.log(itm);
}

This is not the preferred way as we have not checked for hasOwnProperties, we are supposed to iterate only the properties which are its own.

Looping_through_the_items_in_an_Object

Looping_through_the_items_in_an_Object

So let’s rewrite the above code as follows:

for (var itm in thunderbird) {
    if (thunderbird.hasOwnProperty(itm)) {
        console.log(itm + ":" + thunderbird[itm]);
    }
}

Here is the output:

Iteration_with_hasOwnProperty

Iteration_with_hasOwnProperty

We have seen enough about objects right? Any idea how you can delete the property from an object?

delete thunderbird.isMine;
for (var itm in thunderbird) {
    if (thunderbird.hasOwnProperty(itm)) {
        console.log(itm + ":" + thunderbird[itm]);
    }
}

Delete_from_an_object

Delete_from_an_object

Now it is time for a question. What would be the output of the preceding code?

console.log(delete thunderbird.toString);

It will return true, now run it again. What is the output? Again true? This is because toString is an inherited property so it won’t get deleted. So thunderbird.toString will always give you output.

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 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
India India
Microsoft MVP 2016, C# Corner MVP (2014, 2015, 2016), DZone MVB

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Questionfunction calls wrapped inside object Pin
Anirudha_Gohokar6-Mar-17 2:56
memberAnirudha_Gohokar6-Mar-17 2:56 
AnswerRe: function calls wrapped inside object Pin
Sibeesh Passion6-Mar-17 3:08
professionalSibeesh Passion6-Mar-17 3:08 

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