⚙️ JavaScript Setup

Last Updated: 01 Oct 2025

To start writing and running JavaScript, we need to understand file extension, tools, and different ways to run JS code.

📂 File Extension

  • JavaScript files are saved with .js extension.
  • Example: script.js, app.js

🖥 Ways to Run JavaScript

1. Browser Console (Quick Test)

  • Open any browser → Press F12 → Go to Console Tab.
  • Type code directly:
console.log("Hello from JS Console!");

2. Inline Script in HTML

Write JS directly inside <script> tag in an HTML file:

<!DOCTYPE html>
<html>
  <head>
    <title>JS Inline Script</title>
  </head>
  <body>
    <h1>Hello JavaScript!</h1>

    <script>
      console.log("This is inline JavaScript");
    </script>
  </body>
</html>

3. External Script File

Save code in script.js. Link it inside HTML:

<!DOCTYPE html>
<html>
  <head>
    <title>JS External File</title>
  </head>
  <body>
    <h1>Hello External JS!</h1>

    <script src="script.js"></script>
  </body>
</html>

Note: Use of defer Attribute in <script> Tag.

Normally, when you add a <script> tag in HTML, the browser stops loading the page until the script finishes.

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

To avoid this blocking, we can use defer.

It work like this:

  • Script loads in background while HTML continues parsing.
  • Script executes after the HTML is fully loaded
  • Keeps the correct order if multiple scripts have defer.

4. Node.js

  • Download & Install Node.js.
  • Save code in script.js.
  • Run node script.js in terminal.
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