JavaScript Interview_questions: Introduction

Introduction

Javascript is a dynamic scripting language. It is lightweight, cross plateform and most commonly used as a part of web pages, whose implementations allow client-side script to interact with the user and make dynamic pages. It is an interpreted programming language with object-oriented capabilities.

JavaScript was first known as LiveScript, but Netscape changed its name to JavaScript, possibly because of the excitement being generated by Java. JavaScript made its first appearance in Netscape 2.0 in 1995 with the name LiveScript. The general-purpose core of the language has been embedded in Netscape, Internet Explorer, and other web browsers.

Javascript Features:

  • JavaScript is a lightweight, interpreted programming language.
  • Designed for creating network-centric applications.
  • Complementary to and integrated with Java.
  • Complementary to and integrated with HTML.
  • Open and cross-platform

 

Client-side JavaScript:
Client-side JavaScript is the most common form of the language. The script should be included in or referenced by an HTML document for the code to be interpreted by the browser.

The JavaScript client-side mechanism provides many advantages over traditional CGI server-side scripts. For example, you might use JavaScript to check if the user has entered a valid e-mail address in a form field.

JavaScript can be used with any user action on a webpage.

  • Advantages of JavaScript:
  • No server interaction − We can validate user input before sending the page off to the server. This saves server traffic, which means less load on your server.
  • Immediate response to the visitors − They don't have to wait for a page reload to see if they have forgotten to enter something.
  • Increased interactivity − You can create interfaces that react when the user hovers over them with a mouse or activates them via the keyboard.
  • Richer interfaces − You can use JavaScript to include such items as drag-and-drop components and sliders to give a Rich Interface to your site visitors.

Limitations of JavaScript:

  • Client-side JavaScript does not allow the reading or writing of files. This has been kept for security reason.
  • JavaScript cannot be used for networking applications because there is no such support available.
  • JavaScript doesn't have any multithreading or multiprocessor capabilities.
  • Once again, JavaScript is a lightweight, interpreted programming language that allows you to build interactivity into otherwise static HTML pages.

Example:

<html>
   <body>
   
      <script language="javascript" type="text/javascript">
         <!--
            document.write("Hello World!")
         //-->
      </script>
      
   </body>
</html>

 

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