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JavaScript – Placement in HTML File

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JavaScript Placement in HTML File

There is flexibility to place JavaScript code anywhere in an HTML document. However, the most preferred ways to include JavaScript in an HTML file are as follows −

Script in <head>…</head> section.
Script in <body>…</body> section.
Script in <body>…</body> and <head>…</head> sections.
Script in an external file and then include in <head>…</head> section.

You can follow the syntax below to add JavaScript code using the script tag.

<script>
   // JavaScript code
</script>

In the following section, we will see how we can place JavaScript in an HTML file in different ways.

JavaScript in <head>…</head> section

If you want to have a script run on some event, such as when a user clicks somewhere,then you will place that script in the head as follows −

<html>
<head>
   <script type = "text/javascript">
      function sayHello() {
	     alert("Hello World")
	  }
   </script>
</head>

<body>
   <input type = "button" onclick = "sayHello()" value = "Say Hello" />
</body>
</html>

JavaScript in <body>…</body> section

If you need a script to run as the page loads so that the script generates content in the page, then the script goes in the <body> portion of the document. In this case, youwould not have any function defined using JavaScript. Take a look at the following code.

<html>
<head>
</head>
<body>   
   <script type = "text/javascript">
      document.write("Hello World")
   </script>  
   <p>This is web page body </p>   
</body>
</html>

JavaScript in <body> and <head> Sections

You can put your JavaScript code in <head> and <body> sections altogether as follows −

<html>
<head>
   <script type = "text/javascript">
      function sayHello() {
	     alert("Hello World")
	  }
   </script>
</head>
  
<body>
   <script type = "text/javascript">
      document.write("Hello World")
   </script>
   <input type = "button" onclick = "sayHello()" value = "Say Hello" />
</body>
</html>

JavaScript in External File

As you begin to work more extensively with JavaScript, you will likely find cases where you are reusing identical JavaScript code on multiple pages of a site.

You are not restricted to be maintaining identical code in multiple HTML files. The script tag provides a mechanism to allow you to store JavaScript in an external file and then include it in your HTML files.

To use JavaScript from an external file source, you need to write all your JavaScript source code in a simple text file with the extension “.js” and then include that file as shown below.

For example, you can keep the following content in the filename.js file, and then you can use the sayHello function in your HTML file after including the filename.js file.

filename.js

function sayHello() {
   alert("Hello World")
}

External JavaScript file doesn’t contain the <script> tag.

Here is an example to show how you can include an external JavaScript file in your HTML code using the script tag and its src attribute.

You may include the external script reference within the <head> or <body> tag.

<html>
<head>
   <script type = "text/javascript" src = "filename.js" ></script>
</head>
<body>	
   ...
</body>
</html>

Also, you can create different modules to maintain code better and import each module in another JavaScript file or import all modules in a single HTML file.

You can follow the below code to add multiple scripts into a single HTML file.

<head>
  <script src = "filename1.js" ></script>
  <script src = "filename2.js" ></script>
  <script src = "filename3.js" ></script>
</head>

External References

You can add an external JavaScript file in the HTML using the below 3 ways.

1. Using the full file path

When you need to add any hosted JavaScript file or a file that doesn’t exists in the same project into the HTML, you should use the full file path.

For example,

<head>
  <script src = "C://javascript/filename.js" ></script>
</head>

2. Using the relative file path

If you are working on the project and JavaScript and HTML both files are in different folders, you can use the relative file path.

<head>
  <script src = "javascriptfilename.js" ></script>
</head>

3. Using the filename only

If HTML and JavaScript both files are in the same folder, you can use the file name.

<head>
  <script src = "filename.js" ></script>
</head>

Advantages of using the <script> tag

Here are the advantages of using the <script> tag to add JavaScript in the HTML.

Ease of Integration

The <script> tag allows developers to integrate JavaScript into the HTML file easily. Adding JavaScript to the HTML file allows you to add behavior and interactivity to the web page.

Immediate Execution

Whenever the browser finds a <script> tag on the web page, it immediately executes the JavaScript code defined inside that. It enables website visitors to interact with the web pages and get real-time updates immediately.

Inline and External scripts

You can use the <script> tag to add the inline or external script into the HTML file. If you want to load JavaScript before the HTML of a web page, you can add the <script. Tag in the <head> tag. Otherwise, you can add the <script> tag in the <body> tag.

External Libraries and Frameworks integration

The <script> tag enables you to add external libraries and frameworks to the HTML web page.

For example, in the below code, we have added JQuery to the web page using its CDN.

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.7.0/jquery.min.js"> </script>

Here, the “src” attribute contains the hosted link to the library.

Global Scope Access

Whatever code you define in the script tag has access to the global scope of the web page. You can access the global variables, functions, etc., anywhere in the code.

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