How to add JavaScipt to HTML
Overview
JavaScript (JS) is a programming language mainly used alongside HTML and CSS to make websites interactive and add functionality to static web pages by making them more dynamic.
There are two main ways to add JavaScript code to an HTML file. They are as follows:
- Add JavaScript by using HTML
<script>tags. - Link a separate JavaScript file so it can be fetched while rendering the HTML page in the browser.
Add JS using inline HTML
Let's explore the syntax and a code example to understand how we can use <script> tags to add JS to HTML.
Note:
<script>tags allow us to place the JavaScript code anywhere in the HTML file, such as in the<head>and<body>sections of the HTML document.
Syntax
Here's the syntax needed to incorporate JS using inline HTML:
//All JS code must be wrapped using the script tags
<script>
alert('Welcome to educative answers');
</script>
Code
This code snippet below uses the syntax mentioned above:
Explanation
- Line 6: We use the
<img>tag to render the image as seen in the output tab. - Line 7: We create a placeholder,
<div>. This will be populated using the JavaScript code that is defined in the<script>tag after the user clicks on thebuttonelement present on line 8. - Line 8: This line contains the
<button>tag, which listens for theonclickevent and fires thechangecontent()method. - Lines 10–15: We use the
<script>tag. We also use thedocument.getElementById()to get hold of the<div>and populate it using theinnerHTMLproperty as specified in the widget above.
To explore more on
document.getElementById()and theinnerHTMLproperty of JS, please refer to the following links:
Link a separate JS file
Another way to add JS to an HTML file is to link the external JS file with the <script> tag of our HTML file.
The only difference between this method and the one mentioned above is that the JS code now resides in a separate file. This makes it easier to maintain. Moreover, JS files are supported by all modern-day browsers and are often cached, loading the web pages quickly.
Syntax
To import the JS file into HTML, we still have to use the <script> tag but in a different way specified as the following:
<script src='file_path'></script>
The src attribute in the syntax above is used to specify the path to the JS file.
Code
The code widget below illustrates how we can reference a JS file present locally in our directory:
<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" href="style.css">
</head>
<body>
<div class='div-container'>
<p><img src='./logoMarkv2.png'></p>
<div id='content'></div>
<button type="button" onclick="changecontent()">Click me to reveal the name!</button>
</div>
<script src='script.js'></script>
</body>
</html>Explanation
The code now is only maintained in different files and is linked to index.html. Only line 12 is changed in the HTML file.
- Line 12: We use the
<script>tag with thesrcattribute to import the JS code as specified in thescript.jsfile.
Note: This method can also be used to reference files which are present on the internet as specified in the
srcattribute of the<script>tag.
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