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Dynamically changing style
Dynamically changing styles in CSS primarily
involves using JavaScript to interact with the Document Object Model (DOM) and
modify element styles or apply/remove CSS classes.
Here are
common methods for achieving dynamic CSS changes:
1. Directly
manipulating the style property of an element:
This method allows you to set individual CSS
properties directly on an HTML element using JavaScript.
JavaScript
const myElement =
document.getElementById('myDiv');
myElement.style.backgroundColor = 'blue';
myElement.style.fontSize = '20px';
2. Modifying
the className or classList of an element:
This approach involves pre-defining different
styles in CSS classes and then dynamically adding or removing these classes
from elements. This is often preferred for managing more complex style
changes and promoting better separation of concerns.
Code
<div id="myDiv"
class="default-style">Content</div>
Code
.default-style {
color: black;
border: 1px solid gray;
}
.highlighted-style {
color: red;
border: 2px solid blue;
}
JavaScript
const myElement =
document.getElementById('myDiv');
// Add a class
myElement.classList.add('highlighted-style');
// Remove a class
myElement.classList.remove('default-style');
// Toggle a class
myElement.classList.toggle('another-style');
3.
Using setAttribute to modify the style attribute:
You can use setAttribute to directly
change the style attribute of an element. However, be cautious
as this will overwrite any existing inline styles on that element.
JavaScript
const myElement =
document.getElementById('myDiv');
myElement.setAttribute('style', 'background-color: green; padding: 10px;');
4.
Manipulating CSS Custom Properties (CSS Variables):
CSS custom properties, or CSS variables, allow
you to define variables within your CSS and then dynamically change their
values using JavaScript. This provides a powerful way to manage and update
styles globally or for specific components.
Code
:root {
--main-color: blue;
}
.my-box {
background-color: var(--main-color);
}
JavaScript
document.documentElement.style.setProperty('--main-color',
'red');
5. Adding
or removing entire <style> elements:
For more extensive and global style changes, you
can dynamically create or remove <style> elements containing
CSS rules.
JavaScript
const newStyleSheet =
document.createElement('style');
newStyleSheet.innerHTML = 'body { font-family: Arial, sans-serif; }';
document.head.appendChild(newStyleSheet);
The choice of method depends on the specific
requirements of your dynamic styling needs. For simple, isolated changes,
directly manipulating the style property might suffice. For more
complex and maintainable styling, using CSS classes or custom properties with
JavaScript is generally recommended.
Dynamically Changing HTML
Style
To change
the style of an HTML element, use this syntax:
document.getElementById(id).style.property = new
style
The following example changes the style of
a <p> element:
<!DOCTYPE
html>
<html>
<body>
<h2>JavaScript
HTML DOM</h2>
<p>Changing
the HTML style:</p>
<p
id="p1">Hello World!</p>
<p
id="p2">Hello World!</p>
<script>
document.getElementById("p2").style.color
= "blue";
document.getElementById("p2").style.fontFamily
= "Arial";
document.getElementById("p2").style.fontSize
= "larger";
</script>
</body>
</html>
Using Events
The HTML DOM
allows you to execute code when an event occurs.
Events are
generated by the browser when "things happen" to HTML elements:
1.
An
element is clicked on
2.
The
page has loaded
3.
Input
fields are changed
This example
changes the style of the HTML element with id="id1", when the
user clicks a button:
Example
2 <!DOCTYPE
html>
<html>
<body>
<h1
id="id1">My Heading 1</h1>
<button
type="button"
onclick="document.getElementById('id1').style.color
= 'red'">
Click
Me!</button>
</body>
</html>
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