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JavaScript Course | Understanding Code Structure in JavaScript

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  • Difficulty Level : Easy
  • Last Updated : 21 Jan, 2022
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Previous article: JavaScript Course | Printing Hello World in JavaScript 
Inserting JavaScript into a webpage is much like inserting any other HTML content. The tags used to add JavaScript in HTML are <script> and </script>. The code surrounded by the <script> and </script> tags is called a script blog. 
‘type’ attribute was the most important attribute of <script> tag. However, it is no longer used. Browser understands that <script> tag has JavaScript code inside it. 



How to write, run and save code 

Method 1: 

  • Create an html file(.htm) extension and write javascript code inside the ‘script’ tag
  • then simply load the HTML file in the browser

Method 2: 

  • Create a separate javascript file(.js) with .js extension. Write your code in it.
  • Now link this js file with the HTML document using script tag like: 
<script src='relative_path_to_file/file_name.js'></script>
  • either in the body or in the head.

Let’s understand the code structure with the help of a simple javascript example where will make a block disappear with javascript only. 
Code structure: 




<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <script src="script.js"></script>
    <link rel="stylesheet" href="styles.css">
    <title>Button Vanisher</title>
    <a onclick="toggle('plain')">
        <div id="plain">
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The above HTML code contains a simple div element which is wrapped inside an anchor tag(link) so that whenever we click the div element, the javascript code works. Inside the ‘div’ element there’s some random text. Inside the script tag we are linking the javascript file saved as ‘script.js’ with the HTML document. Also the CSS file is linked too. 


#plain {
    border: 2px solid black;
    max-width: 200px;
    height: 300px;
    margin: 0 auto;
    display: block;
a {
    display: block;

The above CSS code only targets two element ‘a’ and ‘div’ element whose ID is ‘plain’. 


// javascript function to change the content of the
function toggle(id) {
    let button = document.getElementById(id);
    if ( == 'block') { = 'none';
    } else { = 'block';

The above Javascript code is called when we click the ‘div’ button, as we have linked them with the ‘a’ tag and also ‘onclick=’toggle(plain)’. Inside the function we are passing the ‘ID’ of the ‘div’ element and then accessing the element from the ‘DOM’ using the getElementByID method and then a simple if-else condition which checks if the ‘div’ is of type ‘block’ then change the display to none, else change it to display block. 
Output: (Before Clicking anywhere on div) 

Output: (After Clicking anywhere on div) 

Learning from the Code 

  • Page is known as document for the purpose of scripting in a web page.
  • Properties of the document can be referenced by writing document followed by a dot, followed by the property name. The document has lots of properties.
  • After <script> tag browser starts to interpret the text as JavaScript until the </script> comes.

The above code is a decent example of how we should make a directory, how to link different types of code files with each other and how to write simple yet effective code. 

Supported Browser:

  • Google Chrome
  • Microsoft Edge
  • Firefox
  • Opera
  • Safari

Next article: JavaScript Course | Variables in JavaScript

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