Example

How To Add JavaScript to HTML

JavaScript, also abbreviated to JS, is a programming language used in web development. As one of the core technologies of the web alongside HTML and CSS, JavaScript is used to make webpages interactive and to build web apps. Modern web browsers, which adhere to common display standards, support JavaScript through built-in engines without the need for additional plugins.

When working with files for the web, JavaScript needs to be loaded and run alongside HTML markup. This can be done either inline within an HTML document or in a separate file that the browser will download alongside the HTML document.

This tutorial will go over how to incorporate JavaScript into your web files, both inline into an HTML document and as a separate file.

Adding JavaScript into an HTML Document

You can add JavaScript code in an HTML document by employing the dedicated HTML tag that wraps around JavaScript code.

The tag can be placed in the section of your HTML or in the section, depending on when you want the JavaScript to load.

Generally, JavaScript code can go inside of the document section in order to keep them contained and out of the main content of your HTML document.

However, if your script needs to run at a certain point within a page’s layout — like when using document.write to generate content — you should put it at the point where it should be called, usually within the section.

Let’s consider the following blank HTML document with a browser title of Today’s Date :

DOCTYPE html> html lang="en-US"> head> meta charset="UTF-8"> meta name="viewport" content="width=device-width, initial-scale=1"> title>Today's Datetitle> head> body> body> html> 

Right now, this file only contains HTML markup. Let’s say we would like to add the following JavaScript code to the document:

let d = new Date(); alert("Today's date is " + d); 

This will enable the webpage to display an alert with the current date regardless of when the user loads the site.

In order to achieve this, we will add a tag along with some JavaScript code into the HTML file.

To begin with, we’ll add the JavaScript code between the tags, signalling the browser to run the JavaScript script before loading in the rest of the page. We can add the JavaScript below the tags, for instance, as shown below:

DOCTYPE html> html lang="en-US"> head> meta charset="UTF-8"> meta name="viewport" content="width=device-width, initial-scale=1"> title>Today's Datetitle> script> let d = new Date(); alert("Today's date is " + d); script> head> body> body> html> 

Once you load the page, you will receive an alert similar to this:

If we were modifying what is shown in the body of the HTML, we would need to implement that after the section so that it displays on the page, as in the example below:

DOCTYPE html> html lang="en-US"> head> meta charset="UTF-8"> meta name="viewport" content="width=device-width, initial-scale=1"> title>Today's Datetitle> head> body> script> let d = new Date(); document.body.innerHTML = "Today's date is " + d + ">" script> body> html> 

The output for the above HTML document loaded through a web browser would look similar to the following:

Scripts that are small or that run only on one page can work fine within an HTML file, but for larger scripts or scripts that will be used on many pages, it is not a very effective solution because including it can become unwieldy or difficult to read and understand. In the next section, we’ll go over how to handle a separate JavaScript file in your HTML document.

Working with a Separate JavaScript File

In order to accommodate larger scripts or scripts that will be used across several pages, JavaScript code generally lives in one or more js files that are referenced within HTML documents, similarly to how external assets like CSS are referenced.

The benefits of using a separate JavaScript file include:

• Separating the HTML markup and JavaScript code to make both more straightforward
• Separate files makes maintenance easier
• When JavaScript files are cached, pages load more quickly

To demonstrate how to connect a JavaScript document to an HTML document, let’s create a small web project. It will consist of script.js in the js/ directory, style.css in the css/ directory, and a main index.html in the root of the project.

project/ ├── css/ | └── style.css ├── js/ | └── script.js └── index.html 

We can start with our previous HTML template from the section above:

DOCTYPE html> html lang="en-US"> head> meta charset="UTF-8"> meta name="viewport" content="width=device-width, initial-scale=1"> title>Today's Datetitle> head> body> body> html> 

Now, let’s move our JavaScript code that will show the date as an header to the script.js file:

let d = new Date(); document.body.innerHTML = "
Today's date is " + d + "
" 

We can add a reference to this script to the section, with the following line of code:

script src="js/script.js">/script> 

The tag is pointing to the script.js file in the js/ directory of our web project.

Let’s consider this line in the context of our HTML file, in this case, within the section:

DOCTYPE html> html lang="en-US"> head> meta charset="UTF-8"> meta name="viewport" content="width=device-width, initial-scale=1"> title>Today's Datetitle> head> body> script src="js/script.js">script> body> html> 

Finally, let’s also edit the style.css file by adding a background color and style to the header:

body  background-color: #0080ff; > h1  color: #fff; font-family: Arial, Helvetica, sans-serif; > 

We can reference that CSS file within the section of our HTML document:

DOCTYPE html> html lang="en-US"> head> meta charset="UTF-8"> meta name="viewport" content="width=device-width, initial-scale=1"> title>Today's Datetitle> link rel="stylesheet" href="css/style.css"> head> body> script src="js/script.js">script> body> html> 

Now, with the JavaScript and CSS in place we can load the index.html page into the web browser of our choice. We should see a page that looks similar to the following:

Now that we’ve placed the JavaScript in a file, we can call it in the same way from additional web pages and update them all in a single location

Conclusion

This tutorial went over how to incorporate JavaScript into your web files, both inline into an HTML document and as a separate .js file.

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Tutorial Series: How To Code in JavaScript

JavaScript is a high-level, object-based, dynamic scripting language popular as a tool for making webpages interactive.

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How do I link a JavaScript file to a HTML file?

How do you properly link a JavaScript file to a HTML document? Secondly, how do you use jQuery within a JavaScript file?

@caramba But what if I need the JS to do something more complicated? I’m trying to have it write a file so I call const fs = require(‘fs’); from node.

6 Answers 6

First you need to download JQuery library from http://jquery.com/ then load the jquery library the following way within your html head tags

then you can test whether the jquery is working by coding your jquery code after the jquery loading script

If you want to use your jquery scripts file seperately you must define the external .js file this way after the jquery library loading.

Test in real time

Thank you SO MUCH. This is exactly the answer that I finally figured out! I know that the question was elementary but I thank you for taking the time to show me this! What I was missing was placing the jQuery library before the javascript file!

Why can’t we put the library after the script? I can place the js script after the HTML element I need to interact though

That’s a great detailed explanation. Just would like to add that you should avoid this Legacy JavaScript MIME types

This is how you link a JS file in HTML

— tag is used to define a client-side script, such as a JavaScript.

type — specify the type of the script

src — script file name and path

To include an external Javascript file you use the tag. The src attribute points to the location of your Javascript file within your web project.

JQuery is simply a Javascript file, so if you download a copy of the file you can include it within your page using a script tag. You can also include Jquery from a content distribution network such as the one hosted by Google.

You can add script tags in your HTML document, ideally inside the which points to your javascript files. Order of the script tags are important. Load the jQuery before your script files if you want to use jQuery from your script.

Then in your javascript file you can refer to jQuery either using $ sign or jQuery . Example:

Below you have some VALID html5 example document. The type attribute in script tag is not mandatory in HTML5.

You use jquery by $ charater. Put libraries (like jquery) in tag — but your script put allways at the bottom of document ( tag) — due this you will be sure that all libraries and html document will be loaded when your script execution starts. You can also use src attribute in bottom script tag to include you script file instead of putting direct js code like above.

       
Im the content
   

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