Programming Basics in JavaScript: Day 2

Introduction

This article will teach you some basic concepts of JavaScript used in Web Applications, like variables, functions, etc.

Before reading this article, I highly recommend reading the previous part,

• Introduction to JavaScript: Day 1

Implementing JavaScript

There are two ways to use JavaScript in your web pages, as follows.

1. Embedding Code in JavaScript

   It is nothing but using an external source file. If you are working on multiple web pages and you want to apply the same JavaScript on other pages also, then you can use the same JavaScript file on multiple web pages. For that use, the "src" attribute of the </script> tag. Just provide the ".js" file to this attribute. Using this, you can reduce the code in HTML web pages. It will help you to hide JavaScript code and share the JavaScript code across multiple HTML documents. It is called as follows.

   The Example for embedding code,

   script.js

   document.write("Welcome, JavaScript World!");

   embedding.html

   <!DOCTYPE html>    
   <html>    
      <title>JavaScript Demo</title>    
      <head>    
      <script src="path\script.js"></script>    
   </head>    
   <body>    
   </body>    
   </html>   

   Output

   When you run this file, it calls the external JavaScript file that will write in the page as follows:

   Welcome, JavaScript World!

2. Inline Code in JavaScript

   It is mainly used when code functionality is small. We place our code between <script>…..</script> tags. And use this tag in our HTML page as follows:

   The following is an example of the Inline Code.

   Inline.html

   <!DOCTYPE html>    
   <html>    
   <title>JavaScript Demo</title>    
   <head></head>    
   <body>    
   <script language="javascript">    
       document.write("Welcome, JavaScript World!");    
   </script>    
   </body>    
   </html>   

   Output

   Welcome, JavaScript World!

JavaScript Programming Basics

Variables in JavaScript

In this JavaScript coding, we use variables to store values. The variable can store several types of data. It is declared using the keyword "var". A variable can store any JavaScript data type like,

• String data
• Numbers
• Boolean values(true/false)

There are the following rules and conventions to declare a variable name,

• It can be upper case or lower case letters.
• Numbers from 0 to 9.
• It cannot start with digits.
• You can use "_" and "$".
• Reserved words or keywords cannot be used.

Example

Var _test(correct)  
Var @jeet(wrong)  

Data Type in JavaScript