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JavaScript - Changing CSS

Changing CSS with JavaScript

JavaScript allows you to change the CSS of the HTML element dynamically.

When HTML gets loaded in the browser, it creates a DOM tree. The DOM tree contains each HTML element in the object format. Furthermore, each HTML element object contains the 'style' object as a property. Here, a 'style' object contains various properties like color, backgroundcolor, etc., to change or get the element's style.

So, you can use various properties of the 'style' object to change the style of the particular HTML element.

Syntax

Follow the syntax below to change the CSS of the HTML element.

element.style.property = value;

In the above syntax, 'element' is an HTML element, which you need to access from the DOM tree. The 'property' is a CSS property, and the 'value' can be static or dynamic.

Example: Changing the style of the HTML element

We have applied the initial style to the div element in the code below. In JavaScript, we change the div element's background color using the style object's 'backgroundColor' property.

<!DOCTYPE html>
<html>
<head>
  <style>
    div {
      background-color: blue;
      width: 700px;
      height: 100px;
      color: white;
    }
  </style>
</head>

<body>
  <div id = "square"> Changing the color of this Div. </div> <br>
  <button onclick="changeColor()"> Change Color </button>
  <script>
    function changeColor() {
      let square = document.getElementById('square');
      square.style.backgroundColor = 'red';
    }
  </script>
</body>
</html>

Example: Adding multiple styles to a single HTML element

In the below code, we change multiple CSS properties of the <div> element in the changeStyle() function.

We use the 'backgroundColor’, 'color’, 'fontSize’, and 'width' properties to change the CSS.

<!DOCTYPE html>
<html>
<body>
  <div id = "square"> Changing the style of this Div. </div> <br>
  <button onclick = "changeStyle()"> Change color </button>
  <script>
    function changeStyle() {
      document.getElementById('square').style.backgroundColor = 'red';
      document.getElementById('square').style.color = "white";
      document.getElementById('square').style.fontSize = "25px";
      document.getElementById('square').style.width = "700px";
    }
  </script>
</body>
</html>

Changing Style of the Element When Event Triggers

You can also change the style of the element when a particular event triggers.

Example

In the below code, we added the 'click' event to the <div> element. When users click the button, it changes the background color of the div element.

<!DOCTYPE html>
<html>
<head>
  <style>
    div {
      width: 700px;
      height: 100px;
      color: white;
      background-color: orange;
    }
  </style>
</head>
<body>
  <div id = "square"> Click Me </div> <br>
  <script>
    const square = document.getElementById('square');
    square.addEventListener('click', () => {
      square.style.backgroundColor = 'green';
      square.style.fontSize = "25px";
    });
  </script>
</body>
</html>

Example

In the below code, we added the 'hover' event on the div element. When the mouse cursor enters and leaves the div element, it changes the style of the div element.

<!DOCTYPE html>
<html>
<head>
  <style>
    div {
      width: 700px;
      height: 100px;
      color: white;
      background-color: orange;
    }
  </style>
</head>
<body>
  <div id = "square"> Hover Me </div> <br>
  <script>
    const square = document.getElementById('square');
    square.addEventListener('mouseenter', () => {
      square.style.backgroundColor = 'green';
      square.style.fontSize = "25px";
    });
    square.addEventListener('mouseleave', () => {
      square.style.backgroundColor = 'orange';
      square.style.fontSize = "initial";
    });
  </script>
</body>
</html>

Changing CSS of HTML elements Dynamically

You can also change the CSS of the HTML element dynamically. You can assign values using the variables.

Example

We have added the default style to the <div> element in the code below.

Also, we have created multiple radio buttons. When users select any radio button, it changes the style of the div element accordingly.

<!DOCTYPE html>
<html>
<head>
<style>
  p {
    width: 700px;
    height: 100px;
    color: white;
    background-color: blue;
  }
</style>
</head>
<body>
<div><p id = "square">Select any of the following colors to change the background color</p></div>
<div>Yellow: <input type = "radio" id = "yellow" name = "color"></div>
<div>Green: <input type = "radio" id = "green" name = "color"></div>
<div>Red: <input type = "radio" id = "red" name = "color"></div>
<script>
  let square = document.getElementById('square');
  //    Changing the style when radio button changes
  let colors = document.getElementsByName('color');
  for (let i = 0; i < colors.length; i++) {
    colors[i].addEventListener('change', function () {
      square.style.backgroundColor = this.id;
    });
 }
</script>
</body>
</html>
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