Introduction to JavaScript

Introduction to JavaScript

In this topic, we have discussed the Introduction to JavaScript as it is a lightweight dynamic programming language. Programs written in this language are called scripts, these scripts are embedded in web pages, and they can manipulate the HTML content. These scripts execute as web pages are loaded; JavaScript’s do not need to have complied to execute. Previously JavaScript was known as LiveScript, but later it was changed to JavaScript.

As Java was very popular at that time and introducing a new language with the similarity in names would be beneficial, they thought. But later, JavaScript became an independent language with its own specification called ECMAScript. Netscape 2.0 is the first where the implementation of JavaScript was first seen. The syntax of JavaScript is more influenced by programming language ‘C.’

Execution of JavaScript

JavaScript is a scripting language, it cannot execute on its own, so we need a platform to execute it. This platform is nothing but the browser where we open the web page; browsers already have built-in execution engines. In earlier times, it was supported mainly by IE(Internet Explorer), so for many sites, there used to be a note for better performance use IE7 or so. But nowadays, all browsers support JavaScript, so we don’t need to bother whether our site will function properly for all browsers or it will be supported by any specific browser only. The Scripts can be executed with the help of the JavaScript engine; the presence of these engines assures the execution of scripts in the browser, server, or any other device.

The name for the engines differ as a browser; some browser embedded engines are called “JavaScript Virtual Machine,” while few others are listed below:

• V8 is Google Chrome’s open-source JavaScript engine developed by Chromium Project.
• SpiderMonkey is the first engine developed by Netscape Communications.
• Nashorn, JScript, Rhino, etc. Are few other JavaScript engines.

Client-Side JavaScript

The most common form of language is Client-Side JavaScript. Browsers need to interpret the scripts; for that, it has to be included or pointed by the HTML document. JavaScript’s included in the HTML; for this it is not mandatory for HTML to be static. But adding scripts, we can make a more interactive webpage.

Client-Side scripts provide advantages over traditional server-side scripts, e.g. we implement JavaScript to validate basic information filled on the webpage such as age for numbers, e-mail for @ and .com, etc. The scripts developed and embedded for validation, are executed once the user submits the form and if the entries are valid form will be submitted else error message will pop up.

Features of Client-Side JavaScript

Given below are the features of client side JavaScript:

• We can Control Document Appearance and Content.
• We can Control the Browser like pop-up boxes.
• Interact with HTML Forms e.g. we can have to submit button.
• Interact with the User e.g. we display messages on a particular text or word.

Why JavaScript is Unique?

There are various tools and programming languages available for the creation of web browsers. JavaScript is distinctive from any of them due to the presence of three features that are uniquely combined. The incorporation of these three features together is made available only in JavaScript and this makes it a unique programming language especially for interface design.

• It provides complete integration with HTML. HTML is a standard tool for the development of web pages. Assimilation of JavaScript brings in powerful libraries and tools to handle most of the required tasks.
• Along with being integrated with HTML, it also is supported by all browsers which makes it the ultimate choice.
• The programming language is efficient with constantly evolving libraries. This makes JavaScript a high-performing programming language in all areas of web, mobile app developments, and even IOT.

Examples of JavaScript

Given below are the examples of JavaScript:

Example #1: Embedded Script

We should keep all our JavaScript code within <script>…..</script> tags, if we are including our code in HTML document. This will distinguish our code from the rest of the code. There are many client-side scripting languages available, it is recommended to specify the scripting language. To do so we just need to add type attribute inside the <script> tag as follows: <script type=“text/javascript”>

Now we will see the example where we have embedded “Hello World!” in the JavaScript as follows:

Code:

<html>
<head>
<title>My First JavaScript code!!!</title>
<script type="text/javascript">
alert("Hello World!");
</script>
</head>
<body>
</body>
</html>

Example #2: External Script

Sometimes we may want a single JavaScript to execute on many other pages, without having to write the same script on every page. To implement this, we can write JavaScript in an external file. After writing we should save the external script with a specific .js extension. The external script should not have <script> or </script> tags. We can make use of this script by pointing to the .js file in the “src” attribute in the <script> tag as follows:

<script src="javascript1.js"></script>

Below is the example of an external script, where we have used javascript1.js as an external file.

Code:

<html>
<head>
<script src="javascript1.js"></script>
</head>
<body>
</body>
</html>

Advantages and Disadvantages of JavaScript

Given below are the advantages and disadvantages mentioned:

Advantages

• Validation of data can be done before sending it to the server. This saves traffic on the server which avoids unnecessary load on a server.
• User-friendly web forms can be created, when users forget to fill or do some mistake they don’t have to wait for the webpage to reload and can be prompted then and there.
• We can create interfaces that guide users when they hover over them via mouse.
• Using JavaScript’s we can add drop-down a list, sliders, etc.
• Date object of JavaScript’s eases working with dates and times.
• Animation and roller over images can be displayed.
• Last modified date of the document can be timestamped using the Document object.

Disadvantages

• Client-Side JavaScript does not allow reading and writing of files, as we cannot allow any random script to arrange our disk.
• Networking applications are not supported by JavaScript.
• Multi-tasking multi-threading is not supported by JavaScript.

Recommended Articles

This has been a guide to Introduction to JavaScript. Here we have discussed the basic concept of JavaScript with execution, characteristics, example, along with advantages of JavaScript. You may also look at the following articles to learn more –

1. TypeScript vs JavaScript
2. JavaScript vs VBScript
3. JavaScript Math Functions
4. JavaScript Tools