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CSS Base

Vendor Prefixing

Add External Stylesheets/Pens

Any URL's added here will be added as <link>s in order, and before the CSS in the editor. If you link to another Pen, it will include the CSS from that Pen. If the preprocessor matches, it will attempt to combine them before processing.

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You're using npm packages, so we've auto-selected Babel for you here, which we require to process imports and make it all work. If you need to use a different JavaScript preprocessor, remove the packages in the npm tab.

Add External Scripts/Pens

Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

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Use npm Packages

We can make npm packages available for you to use in your JavaScript. We use webpack to prepare them and make them available to import. We'll also process your JavaScript with Babel.

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Code Indentation


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Auto-Updating Preview

If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.

HTML Settings

Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

              // The data object (or state)
var data = {
	listName: 'Starting at Hogwarts',
	todos: []

// The state-based UI
var template = function (data) {

	// Create the list heading
	var html = '<h1>' + data.listName + '</h1>';

	// If there are no list items, show a message
	// Otherwise, display the list items
	if (data.todos.length < 1) {
		html += '<p><em>You do not have any items to complete yet. Please add some.</em></p>';
	} else {
		html += '<ul>' + (todo) {
			return '<li>' + todo + '</li>';
		}).join('') + '</ul>';

	// Return the template
	return html;


 * Sanitize and encode all HTML in a user-submitted string
 * (c) 2018 Chris Ferdinandi, MIT License,
 * @param  {String} str  The user-submitted string
 * @return {String} str  The sanitized string
var sanitizeHTML = function (str) {
	var temp = document.createElement('div');
	temp.textContent = str;
	return temp.innerHTML;

 * Create an immutable copy of an object and recursively encode all of its data
 * @param  {*} obj The object to clone
 * @return {*}     The immutable, encoded object
var clone = function (obj) {

	// Get the object type
	var type =, -1).toLowerCase();

	// If an object, loop through and recursively encode
	if (type === 'object') {
		var cloned = {};
		for (var key in obj) {
			if (obj.hasOwnProperty(key)) {
				cloned[key] = clone(obj[key]);
		return cloned;

	// If an array, create a new array and recursively encode
	if (type === 'array') {
		return (item) {
			return clone(item);

	// If the data is a string, encode it
	if (type === 'string') {
		return sanitizeHTML(obj);

	// Otherwise, return object as is
	return obj;


 * Reactivity update the data object
 * @param {Object} obj The data to update
var setData = function (obj) {
	for (var key in obj) {
		if (obj.hasOwnProperty(key)) {
			data[key] = obj[key];
  var sanitized = clone(data);
	app.innerHTML = template(sanitized);

// Render the initial UI
var app = document.querySelector('#app');
app.innerHTML = template(clone(data));

// Uncomment this to update the UI
// You can also open up the console feature and run it there
setData({todos: [
	'Fix my wand',
	'Buy new robes',
	'Enroll in courses'
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