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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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Using packages here is powered by esm.sh, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ESM usage.

All packages are different, so refer to their docs for how they work.

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HTML 

              
                <div class="container my-4">
   

<h1>Defer image loading script</h1>
<p>If you have large images in a carousel, it would be a good idea to defer loading them. This will increase your page load time. This scripts adds a base 64 image placheholder in the html and then uses javascript to replace that with the actual image source. So the document loads and then loads in the images.</p>
   
   <p>
      <a href="https://developers.google.com/web/tools/chrome-devtools/network-performance/network-conditions">How to simulate a slow connection in Google DevTools</a>
   </p>
   
<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAABlBMVEXR0dG/v7+g+VsXAAAACXBIWXMAAA7EAAAOxAGVKw4bAAAACklEQVQImWNgAAAAAgAB9HFkpgAAAABJRU5ErkJggg==" data-src="https://resi.ze-robot.com/dl/aw/awesome-mountain-wallpaper-1920%C3%971080.jpg" class="img-defer">

</div>
!

CSS 

              
                /* 
Create base 64 images
https://www.base64-image.de/
*/
.img-defer {
   display:inline-block;
   width:100%;
   /*  Set a min-height of image   */
   min-height:100px;
}
!

JS 

              
                
function init() {
var imgDefer = document.getElementsByClassName('img-defer');
for (var i=0; i<imgDefer.length; i++) {
if(imgDefer[i].getAttribute('data-src')) {
imgDefer[i].setAttribute('src',imgDefer[i].getAttribute('data-src'));
} } }
window.onload = init;
!
999px

Console