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JS Introduction

This JavaScript tutorial is designed for beginners as well as professionals.
JS is one of the most widely used programming language and it is easy to learn.

What is JavaScript?

JavaScript is a client-side scripting language and it is used to enhance the interaction of the user with the webpage.
In other words, you can make your webpage more lively and interactive using JavaScript.
The implementation of JavaScript is very easy because it is integrated with HTML.

Application of JavaScript:

  • Client-side validation
  • Dynamic drop-down menus
  • Displaying date and time
  • Displaying pop-up windows and dialog boxes
  • Validate user input in an HTML form before sending the data to a server
  • Displaying clocks etc

Why to Learn Javascript:

JavaScript is one of the three languages that every web developer must learn:
  1. HTML is used to define the content of the webpage.
  2. CSS is used to specify the layout of the webpage.
  3. JavaScript is used to program the behavior of the webpage.

JavaScript Example:

Example:

<!DOCTYPE html>
<html>
<body>
<p id="trial"> JavaScript Example </p>
<button type="button" onclick='document.getElementById("trial").innerHTML = "Learn JavaScript!"'> Click Me! </button>
</body>
</html>
Try it

Where to put JavaScript code?

You can put your JS code in three places:
  • Between the body tag of HTML
  • Between the head tag of HTML
  • In .js file (external javaScript)

What JavaScript can do?

You can change the HTML content using Javascript. In the below example, HTML content is changed using getElementById() method.

Example:

<!DOCTYPE html>
<html>
<body>
<p id="trial"> JavaScript to change HTML content. </p>
<button type="button" onclick='document.getElementById("trial").innerHTML = "Learn JavaScript!"'> Click here </button>
</body>
</html>
Try it
JavaScript accepts both double and single quotes.

Example:

<!DOCTYPE html>
<html>
<body>
<p id="trial"> JavaScript to change HTML content. </p>
<button type="button" onclick="document.getElementById('trial').innerHTML = 'LearnJavaScript!'"> Click here </button>
</body>
</html>
Try it

JavaScript Can Change HTML Attribute Values:

You can change HTML attribite values using JS.
The following example changes the value of the src (source) attribute of an <img> tag using JS.

Example:

<!DOCTYPE html>
<html>
<body>
<script>
function technology(sw) {
var pic;
if (sw == 0) {
pic = "css-2.jpg"
} else {
pic = "html.jpg"
}
document.getElementById('myImage').src = pic;
}
</script>
<img id="myImage" src="html.jpg" alt="js - html" width="500" height="280">
<p>
<button type="button" onclick="technology(1)"> Learn HTML </button>
<button type="button" onclick="technology(0)"> Learn CSS </button>
</p>
</body>
</html>
Try it

JavaScript to Change HTML Styles (CSS):

You can chanage the style of an HTML element using JS.

Example:

<!DOCTYPE html>
<html>
<body>
<p id="trial"> HTML stands for Hypertext Markup Language </p>
<script>
function myFunction() {
document.getElementById("trial").style.fontSize = "30px";
document.getElementById("trial").style.color = "#fff";
document.getElementById("trial").style.backgroundColor = "#ff5722";
document.getElementById("trial").style.padding = "15px";
}
</script>
<button type="button" onclick="myFunction()"> Click Me! </button>
</body>
</html>
Try it

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