Introduction to Javascript

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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 JavaScripts 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.

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• 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.

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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 dont 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.

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• 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 Chromes 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.

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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. JavaScripts
  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 _at_ 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.

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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.

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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.

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• 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.

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Examples of Javascript

• Example 1
• Embedded Script.
• We should keep all our JavaScript code within
  ltscriptgt..lt/scriptgt 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 ltscriptgt tag as follows
  ltscript typetext/javascriptgt

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

• Code
• lthtmlgt
• ltheadgt
• lttitlegtMy First JavaScript code!!!lt/titlegt
• ltscript type"text/javascript"gt
• alert("Hello World!")
• lt/scriptgt
• lt/headgt
• ltbodygt
• lt/bodygt
• lt/htmlgt

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