How to add JavaScript to a Web Page
A webpage can include JavaScript by connecting to different files or embedding it into HTML. Browsers that support JavaScript can run the code and give functionalities beyond static content, utilizing these methods. JavaScript is an interpreted language, which means that scripts run without first requiring compilation, and is typically integrated straight into HTML pages.
The following are the main methods for adding JavaScript to an HTML page:
Directly in HTML (Inline): JavaScript code can be inserted straight between the HTML document’s opening <script> and closing </script> JavaScript code can be inserted straight between the HTML document’s opening <script> elements. When the browser processes the tag, the JavaScript code is automatically executed. Script tags can be placed practically anywhere in an HTML text. You may put it in the <head> or <body> sections, for example.
The browser console would report “Hi there!” and show “The content of the webpage” in this case.
- Linking an External File: The src element of the <script> tag allows you to link your JavaScript code to your HTML page while maintaining it in a different file (usually with a.js extension). Usually, this tag appears at the conclusion of the <body> or in the <head>. or.
- It’s generally accepted that using external JavaScript files is best practice. It improves code organisation and facilitates maintenance by keeping behaviour (JavaScript) and text (HTML) distinct. Using the src tag enables you to keep only one copy of the JavaScript code when it is shared across several web pages. Additionally, the browser only needs to download external files once, and they can be recovered from the cache for later pages, which can speed up load times. The src property and inline code cannot be contained in the same<script> tag.
- In an HTML Event Handler Attribute: HTML event handler properties like onclick, onmouseover, and onload can all contain JavaScript code.
- Although this technique was popular in the early days of the internet, it is now seldom ever utilised in JavaScript.
- In a URL using the JavaScript: Protoco: Although it is mentioned as a method of embedding JavaScript, current code hardly ever uses a URL that uses the unique JavaScript: protocol.
Placement and Execution Order
Typically, scripts execute in the document’s order of appearance. When the code is run in relation to the loading and parsing of the rest of the page depends on where the <script> tag is located in the HTML document.
- When inserted in the <head> , scripts are performed before the <body> content. When scripts in the attempt to access or modify elements in the <body> before loading, errors may occur.
- Scripts are usually placed before the closing </body> element at the bottom of HTML files. This guarantees that all DOM elements are accessible for the script to work with and that the HTML content has been completely loaded and parsed. While some scripts may perform substantial work in the first loading phase, others may build functions and register event handlers in the first loading phase and then do nothing in the second.
- The default execution order and timing can be changed using attributes like async and defer. Without interfering with the HTML parser, asynchronous scripts (async) download in the background and run as soon as they can. Although they also download in the background, deferred scripts (defer) don’t run until the page has been completely parsed.
Compatibility Notes
The <script> tag had to contain a type attribute, often type=”text/javascript,” according to prior HTML standards (HTML4), but modern HTML does not require this any more. Additionally, it was common practice to enclose the JavaScript code inside HTML comment tags (!–… //–>) inside the SCRIPT> tag for compatibility with earlier browsers that did not support JavaScript. This instructed the script block to be ignored by outdated browsers.
In general, the most widely used and advised methods for adding JavaScript include embedding code directly within <script> tags for small snippets or utilising the src property to connect other files. To work with JavaScript on web pages and create dynamic web content, it is essential to grasp these methods and the function of the Document Object Model (DOM).