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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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Adding Classes

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About the <head>

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!
Insecure Resource

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CSS

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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

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JavaScript

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

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Babel includes JSX processing.

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HTML 

              
                <main>
	<h1>Different ways to call (or not call) <code>classList.remove()</code></h1>
	<p>Each of these boxes starts with 3 classes defining different background colors. If our call to <code>classList.remove()</code> works, it should fall back to a simple gray color. Otherwise, it will either display yellow, green, or blue.</p>
	<p>Open your DevTools to see how each either succeeds or fails depending on the syntax and browser.</p>

	<h2>Fails because "invalid characters"</h2>
	<code><pre>// 😭 "Invalid characters" / can't include spaces
thing1.classList.remove('class1 class2 class3');</pre></code>
	<div id="thing1" class="class1 class2 class3"></div>

	<h2>Works in modern browsers (not IE)</h2>
	<code><pre>// 😎 Modern
thing2.classList.remove('class1', 'class2', 'class3');</pre></code>
	<p class="warning"><strong>Warning</strong>: Doesn't work in Internet Explorer.</p>
	<div id="thing2" class="class1 class2 class3"></div>

	<h2>Works in Internet Explorer</h2>
	<code><pre>// 🤓 Internet Explorer
thing3.classList.remove('class1');
thing3.classList.remove('class2');
thing3.classList.remove('class3');</pre></code>
	<div id="thing3" class="class1 class2 class3"></div>
	
	<h2>References</h2>
	<ul>
		<li><a href="https://developer.mozilla.org/en-US/docs/Web/API/Element/classList#Browser_compatibility" target="_blank" rel="noopener">MDN: Element.classList</a></li>
	</ul>
</main>
!

CSS 

              
                /* ------------------------------ */
/* Base                           */
/* ------------------------------ */

html {
	box-sizing: border-box;
}

*,
::after,
::before {
	box-sizing: inherit;
}

body {
	margin: 1rem auto 3rem;
	line-height: 1.4;
	tab-size: 4;
}

main {
	display: block; /* Fix IE rendering main as inline */
	margin: 0 auto;
	max-width: 38rem;
	padding-left: 1rem;
	padding-right: 1rem;
}

pre {
	border: 1px solid #ccc;
	padding: 1rem;
	overflow: auto;
	-webkit-overflow-scroll: touch;
}

.warning {
	color: red;
	font-size: 0.8rem;
}

/* ------------------------------ */
/* Demo                           */
/* ------------------------------ */

div { width: 100px; height: 100px; }
div { background: gray; }

.class1 { background: yellow; }
.class2 { background: green; }
.class1 { background: blue; }
!

JS 

              
                // 😭 "Invalid characters" / can't include spaces
try {
	thing1.classList.remove('class1 class2 class3');
} catch (err) {
	console.log(err);
}

// 😎 Modern
thing2.classList.remove('class1', 'class2', 'class3');

// 🤓 Internet Explorer
thing3.classList.remove('class1');
thing3.classList.remove('class2');
thing3.classList.remove('class3');
!
999px

Console