<script> Tag : JavaScript code must be located between opening and closing script tags ; <script> and </script> tags.
<!DOCTYPE html>
 <html>
 <body>
<h1>JavaScript Basics</h1>
<p id="ex"></p>
<script>
 document.getElementById("ex").innerHTML = "Hello World! This Is My First JavaScript";
 </script>
</body>
 </html>
Output :

Block of JavaScript code that can be executed when “called” is a JS Function and when user clicks a button an Event is occured and function can be called.
JS in HTML<head> section:
JavaScript function is kept in HTML page’s <head> section.When a button is clicked this function is called.
<!DOCTYPE html>
 <html>
 <head>
 <script>
 function myFunction() {
 document.getElementById("ex").innerHTML = "Projects, Tutorials & More!";
 }
 </script>
 </head>
<body>
 <h1>JS in Head Section</h1>
 <p id="ex">Code Projects</p>
 <button type="button" onclick="myFunction()">Try It!</button>
</body>
 </html>
Output :


JS in HTML<body> section :
JavaScript function is kept in HTML page’s <body> section.When a button is clicked this function is called.
<!DOCTYPE html>
 <html>
 <body>
<h1>JS in Body Section</h1>
 <p id="ex">Code Projects</p>
 <button type="button" onclick="myFunction()">Try it!</button>
<script>
 function myFunction() {
 document.getElementById("ex").innerHTML = "Projects, Tutorials & More";
 }
 </script>
</body>
 </html>
Output :


External JS Files :
( script.js )
function myFunction() {
 document.getElementById("ex").innerHTML = "Projects, Tutorials & More";
 }
JavaScript is used external when the same code is used in many different pages. JavaScript files have ( .js ) extension.
Insert name of script file in src (source) attribute of a <script> tag to use External JS:
Check this out!
<!DOCTYPE html> <html> <body> <h1>External JavaScript</h1> <p id="ex">Code Projects</p> <button type="button" onclick="myFunction()">Try it</button> <p> <i> NOTE :myFunction() is stored in an external file named "scripts.js" </i> </p> <script src="script.js"></script> </body> </html>
Output :


