JavaScript Closures Example

YatinDecember 13th, 2018Last Updated: December 14th, 2018

2 60 4 minutes read

Greetings readers, in this tutorial, we will understand Closures in the JavaScript language.

1. Introduction

JavaScript is an object-oriented programming language that allows the client-side scripting to interact with a user and deliver the dynamic pages. Most web browsers including Google Chrome, Mozilla Firefox, Safari, Internet Explorer, Microsoft Edge, Opera, etc. support it. The JavaScript scripting language includes:

Declaring variables
Maintaining the retrieving values
Defining and invoking functions
Defining classes
Load and use external modules
Define event handlers
And much more ….

1.1 Advantages of JavaScript Language

The pros of using the JavaScript scripting language are:

JavaScript is easy to learn
It executes on client’s browser, so eliminates the server-side processing and be executed on any OS
JavaScript can be used with any type of web page e.g. PHP, ASP.NET, Perl etc
Web-page performance increases due to client-side execution
JavaScript code can be minified to decrease the loading time from the server
Many JavaScript-based application frameworks are available in the market to create Single page web applications e.g. AngularJS, ReactJS etc.

1.2 Disadvantages of JavaScript Language

The cons of using the JavaScript scripting language are:

No support for networking applications
Does not have any multi-threading or multi-processing capabilities
Does not allow the file reading and writing capabilities

1.3 Closures in JavaScript Language

It is an inner function that has access to outer function’s variables and parameters in addition to its own and global variables
Users can create a closure by defining a function inside another function
The scope of the closure is defined statically by its location within the source code
Usage:
- - Maintain a private reference to a variable in the outer scope

2. JavaScript Closures Example

Here is a systematic guide for implementing this tutorial using the JavaScript language.

2.1 Tools Used

We are using Eclipse Kepler SR2, JDK 8 and Maven. Having said that, we have tested the code against JDK 1.7 and it works well.

2.2 Project Structure

Firstly, let us review the final project structure if you are confused about where you should create the corresponding files or folder later!

JavaScript Closures - Application Project Structure — Fig. 1: Application Project Structure

2.3 Project Creation

This section will show on how to create a Java-based Maven project with Eclipse. In Eclipse Ide, go to File -> New -> Maven Project.

JavaScript Closures - Create a Maven Project — Fig. 2: Create a Maven Project

In the New Maven Project window, it will ask you to select the project location. By default, ‘Use default workspace location’ will be selected. Just click on the next button to proceed.

JavaScript Closures - Project Details — Fig. 3: Project Details

Select the ‘Maven Web App’ Archetype from the list of options and click next.

JavaScript Closures - Archetype Selection — Fig. 4: Archetype Selection

It will ask you to ‘Enter the group and the artifact id for the project’. We will input the details as shown in the below image. The version number will be by default: 0.0.1-SNAPSHOT.

JavaScript Closures - Archetype Parameters — Fig. 5: Archetype Parameters

Click on Finish and the creation of a maven project is completed. If you see, it has downloaded the maven dependencies and a pom.xml file will be created. It will have the following code:

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.javascript</groupId>
	<artifactId>JavascriptClosures</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>war</packaging>
</project>

3. Application Building

Let us create an application to understand the basic building blocks of this tutorial.

3.1 Define the HTML

Let us write a simple index page in the JavascriptClosures/src/main/webapp/ folder. Add the following code to it:

index.jsp

<!-- Javascript closures tutorial -->
<div id="title">
	<h4 class="text-info">What is a Closure?</h4>
	<ul>
		<li>It is an inner function that has access to outer function's variables and parameters in addition to it's own and global variables.</li>
		<li>Users can create a closure by defining a function inside another function.</li>
		<li>The scope of the closure is defined statically by its location within the source code.</li>
		<li>Usage:
				<ul>
					<li>Maintain a private reference to a variable in the outer scope.</li>
				</ul>
		</li>
	</ul>
</div>
<div> </div>

<button id="btn_submit" type="button" class="btn btn-success" onclick="clicks();">Click me</button>
<div> </div>

<div id="result"></div>

3.2 Define the JavaScript function

Let us write a simple javascript function that will help developers understand the closures in the javascript language. Add the following code to it:

JavaScript function

var clicks = (function () 
{
	var count = 0;
	return function() {
		document.getElementById("result").innerHTML = ++count;
	}
})();

3.3 First application

Complete the above steps and save the file. Let us see the sample code snippet.

index.jsp

<!DOCTYPE html>
<html lang="en">

<head>
    <title>Index page</title>
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
    <link rel="stylesheet" href="https://www.webcodegeeks.com/wp-content/litespeed/localres/aHR0cHM6Ly9zdGFja3BhdGguYm9vdHN0cmFwY2RuLmNvbS8=bootstrap/4.1.3/css/bootstrap.min.css">
</head>

<body>
    <div class="container">
        <h2 align="center" class="text-danger">Closures in JavaScript</h2>
        <hr />

        <!-- Javascript closures tutorial -->
		<div id="title">
			<h4 class="text-info">What is a Closure?</h4>
			<ul>
				<li>It is an inner function that has access to outer function's variables and parameters in addition to it's own and global variables.</li>
				<li>Users can create a closure by defining a function inside another function.</li>
				<li>The scope of the closure is defined statically by its location within the source code.</li>
				<li>Usage:
						<ul>
							<li>Maintain a private reference to a variable in the outer scope.</li>
						</ul>
				</li>
			</ul>
		</div>
		<div> </div>
		
		<button id="btn_submit" type="button" class="btn btn-success" onclick="clicks();">Click me</button>
		<div> </div>
		
		<div id="result"></div>
    </div>
    <script>
		var clicks = (function () 
		{
			var count = 0;
			return function() {
				document.getElementById("result").innerHTML = ++count;
			}
		})();
    </script>
</body>

</html>

4. Run the Application

As we are ready for all the changes, let us compile the project and deploy the application on the Tomcat7 server. To deploy the application on Tomat7, right-click on the project and navigate to Run as -> Run on Server.

JavaScript Closures - Deploy Application on Tomcat — Fig. 6: How to Deploy Application on Tomcat

Tomcat will deploy the application in its web-apps folder and shall start its execution to deploy the project so that we can go ahead and test it in the browser.

5. Project Demo

Open your favorite browser and hit the following URL to display the application’s index page as shown in Fig. 7.

http://localhost:8082/JavascriptClosures/

Server name (localhost) and port (8082) may vary as per your Tomcat configuration.

JavaScript Closures - Index page — Fig. 7: Index page

Users can click the button to display and increment the click counter. That is all for this tutorial and I hope the article served you whatever you were looking for. Happy Learning and do not forget to share!

6. Conclusion

In this section, developers learned how to create a simple application with the JavaScript language. Developers can download the sample application as an Eclipse project in the Downloads section.

7. Download the Eclipse Project

This was a beginners tutorial to understand the closures in the javascript language.

Download
You can download the full source code of this example here: JavascriptClosures

JavaScript Closures Example

1. Introduction

Thank you!

1.1 Advantages of JavaScript Language

1.2 Disadvantages of JavaScript Language

1.3 Closures in JavaScript Language

2. JavaScript Closures Example

2.1 Tools Used

2.2 Project Structure

2.3 Project Creation

3. Application Building

3.1 Define the HTML

3.2 Define the JavaScript function

3.3 First application

4. Run the Application

5. Project Demo

6. Conclusion

7. Download the Eclipse Project

Thank you!

Yatin

Thank you!

1. Introduction

Thank you!

1.1 Advantages of JavaScript Language

1.2 Disadvantages of JavaScript Language

1.3 Closures in JavaScript Language

2. JavaScript Closures Example

2.1 Tools Used

2.2 Project Structure

2.3 Project Creation

3. Application Building

3.1 Define the HTML

3.2 Define the JavaScript function

3.3 First application

4. Run the Application

5. Project Demo

6. Conclusion

7. Download the Eclipse Project

Thank you!

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