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.
In CodePen, whatever you write in the HTML editor is what goes within the <body>
tags in a basic HTML5 template. So you don't have access to higher-up elements like the <html>
tag. If you want to add classes there that can affect the whole document, this is the place to do it.
In CodePen, whatever you write in the HTML editor is what goes within the <body>
tags in a basic HTML5 template. If you need things in the <head>
of the document, put that code here.
The resource you are linking to is using the 'http' protocol, which may not work when the browser is using https.
CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.
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.
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-
.
We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).
Any URLs added here will be added as <link>
s in order, and before the CSS in the editor. You can use the CSS from another Pen by using its URL and the proper URL extension.
You can apply CSS to your Pen from any stylesheet on the web. Just put a URL to it here and we'll apply it, in the order you have them, before the CSS in the Pen itself.
You can also link to another Pen here (use the .css
URL Extension) and we'll pull the CSS from that Pen and include it. If it's using a matching preprocessor, use the appropriate URL Extension and we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.
JavaScript preprocessors can help make authoring JavaScript easier and more convenient.
Babel includes JSX processing.
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.
You can apply a script from anywhere on the web to your Pen. Just put a URL to it here and we'll add it, in the order you have them, before the JavaScript in the Pen itself.
If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.
You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.
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.
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.
If you're using React / ReactDOM, make sure to turn on Babel for the JSX processing.
If active, Pens will autosave every 30 seconds after being saved once.
If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.
If enabled, your code will be formatted when you actively save your Pen. Note: your code becomes un-folded during formatting.
Visit your global Editor Settings.
<h2>Example of weird error message placement</h2>
<form novalidate>
<div>
<label class="label-normal">
<input type="radio" name="radio" class="error" id="radio-1">
<div class="error-message">This is a weird place for an error message</div>
Yes
</label>
<label class="label-normal">
<input type="radio" name="radio" class="error" id="radio-2">
No
</label>
<div class="error-message">It really belongs here.</div>
</div>
<input type="submit" class="button" value="Submit">
</form>
<h2>Try It Out</h2>
<p>Tab through the form fields to see it in action.</p>
<form class="validate">
<div>
<label for="text">Name</label>
<input type="text" id="text" required>
</div>
<div>
<label for="email">Email</label>
<input type="email" id="email" title="The domain portion of the email address is invalid (the portion after the @)." pattern="^([^\x00-\x20\x22\x28\x29\x2c\x2e\x3a-\x3c\x3e\x40\x5b-\x5d\x7f-\xff]+|\x22([^\x0d\x22\x5c\x80-\xff]|\x5c[\x00-\x7f])*\x22)(\x2e([^\x00-\x20\x22\x28\x29\x2c\x2e\x3a-\x3c\x3e\x40\x5b-\x5d\x7f-\xff]+|\x22([^\x0d\x22\x5c\x80-\xff]|\x5c[\x00-\x7f])*\x22))*\x40([^\x00-\x20\x22\x28\x29\x2c\x2e\x3a-\x3c\x3e\x40\x5b-\x5d\x7f-\xff]+|\x5b([^\x0d\x5b-\x5d\x80-\xff]|\x5c[\x00-\x7f])*\x5d)(\x2e([^\x00-\x20\x22\x28\x29\x2c\x2e\x3a-\x3c\x3e\x40\x5b-\x5d\x7f-\xff]+|\x5b([^\x0d\x5b-\x5d\x80-\xff]|\x5c[\x00-\x7f])*\x5d))*(\.\w{2,})+$" required>
</div>
<div>
<label for="url">URL</label>
<input type="url" id="url" title="The URL is a missing a TLD (for example, .com)." pattern="^(?:(?:https?|HTTPS?|ftp|FTP):\/\/)(?:\S+(?::\S*)?@)?(?:(?!(?:10|127)(?:\.\d{1,3}){3})(?!(?:169\.254|192\.168)(?:\.\d{1,3}){2})(?!172\.(?:1[6-9]|2\d|3[0-1])(?:\.\d{1,3}){2})(?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}(?:\.(?:[1-9]\d?|1\d\d|2[0-4]\d|25[0-4]))|(?:(?:[a-zA-Z\u00a1-\uffff0-9]-*)*[a-zA-Z\u00a1-\uffff0-9]+)(?:\.(?:[a-zA-Z\u00a1-\uffff0-9]-*)*[a-zA-Z\u00a1-\uffff0-9]+)*(?:\.(?:[a-zA-Z\u00a1-\uffff]{2,}))\.?)(?::\d{2,5})?(?:[/?#]\S*)?$" required>
</div>
<div>
<strong>Radio Buttons</strong>
<label class="label-normal">
<input type="radio" name="radio" id="radio-1" required>
Yes
</label>
<label class="label-normal">
<input type="radio" name="radio" id="radio-2" required>
No
</label>
</div>
<input type="submit" class="button" value="Submit">
</form>
body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif;
font-size: 112.5%;
margin-left: auto;
margin-right: auto;
max-width: 40em;
width: 88%;
}
/**
* Form Styles
*/
label {
display: block;
font-weight: bold;
margin-bottom: 0.5em;
}
.label-normal {
font-weight: normal;
}
.description-date {
color: #808080;
font-size: 0.8em;
font-weight: normal;
}
.supports-date .description-date {
display: none;
}
input,
select {
display: inline-block;
font-size: 1em;
margin-bottom: 1em;
padding: 0.25em 0.5em;
width: 100%;
}
[type="checkbox"],
[type="radio"] {
margin-bottom: 0.5em;
width: auto;
}
.button {
background-color: #0088cc;
border: 1px solid #0088cc;
border-radius: 1px;
color: #ffffff;
display: inline-block;
font-size: 0.9375em;
font-weight: normal;
line-height: 1.2;
margin-right: 0.3125em;
margin-bottom: 0.3125em;
padding: 0.5em 0.6875em;
width: auto;
}
.button:active,
.button:focus,
.button:hover {
background-color: #005580;
border-color: #005580;
color: #ffffff;
text-decoration: none;
}
.button:active {
box-shadow: inset 0 0.15625em 0.25em rgba(0, 0, 0, 0.15), 0 1px 0.15625em rgba(0, 0, 0, 0.05);
}
/**
* Errors
*/
.error {
border-color: red;
}
.error-message {
color: red;
font-style: italic;
margin-bottom: 1em;
}
// Add the novalidate attribute when the JS loads
var forms = document.querySelectorAll('.validate');
for (var i = 0; i < forms.length; i++) {
forms[i].setAttribute('novalidate', true);
}
// Validate the field
var hasError = function (field) {
// Don't validate submits, buttons, file and reset inputs, and disabled fields
if (field.disabled || field.type === 'file' || field.type === 'reset' || field.type === 'submit' || field.type === 'button') return;
// Get validity
var validity = field.validity;
// If valid, return null
if (validity.valid) return;
// If field is required and empty
if (validity.valueMissing) return 'Please fill out this field.';
// If not the right type
if (validity.typeMismatch) {
// Email
if (field.type === 'email') return 'Please enter an email address.';
// URL
if (field.type === 'url') return 'Please enter a URL.';
}
// If too short
if (validity.tooShort) return 'Please lengthen this text to ' + field.getAttribute('minLength') + ' characters or more. You are currently using ' + field.value.length + ' characters.';
// If too long
if (validity.tooLong) return 'Please shorten this text to no more than ' + field.getAttribute('maxLength') + ' characters. You are currently using ' + field.value.length + ' characters.';
// If number input isn't a number
if (validity.badInput) return 'Please enter a number.';
// If a number value doesn't match the step interval
if (validity.stepMismatch) return 'Please select a valid value.';
// If a number field is over the max
if (validity.rangeOverflow) return 'Please select a value that is no more than ' + field.getAttribute('max') + '.';
// If a number field is below the min
if (validity.rangeUnderflow) return 'Please select a value that is no less than ' + field.getAttribute('min') + '.';
// If pattern doesn't match
if (validity.patternMismatch) {
// If pattern info is included, return custom error
if (field.hasAttribute('title')) return field.getAttribute('title');
// Otherwise, generic error
return 'Please match the requested format.';
}
// If all else fails, return a generic catchall error
return 'The value you entered for this field is invalid.';
};
// Show an error message
var showError = function (field, error) {
// Add error class to field
field.classList.add('error');
// If the field is a radio button and part of a group, error all and get the last item in the group
if (field.type === 'radio' && field.name) {
var group = document.getElementsByName(field.name);
if (group.length > 0) {
for (var i = 0; i < group.length; i++) {
// Only check fields in current form
if (group[i].form !== field.name) continue;
group[i].classList.add('error');
}
field = group[group.length - 1];
}
}
// Get field id or name
var id = field.id || field.name;
if (!id) return;
// Check if error message field already exists
// If not, create one
var message = field.form.querySelector('.error-message#error-for-' + id );
if (!message) {
message = document.createElement('div');
message.className = 'error-message';
message.id = 'error-for-' + id;
// If the field is a radio button or checkbox, insert error after the label
var label;
if (field.type === 'radio' || field.type ==='checkbox') {
label = field.form.querySelector('label[for="' + id + '"]') || field.parentNode;
if (label) {
label.parentNode.insertBefore( message, label.nextSibling );
}
}
// Otherwise, insert it after the field
if (!label) {
field.parentNode.insertBefore( message, field.nextSibling );
}
}
// Add ARIA role to the field
field.setAttribute('aria-describedby', 'error-for-' + id);
// Update error message
message.innerHTML = error;
// Show error message
message.style.display = 'block';
message.style.visibility = 'visible';
};
// Remove the error message
var removeError = function (field) {
// Remove error class to field
field.classList.remove('error');
// Remove ARIA role from the field
field.removeAttribute('aria-describedby');
// If the field is a radio button and part of a group, remove error from all and get the last item in the group
if (field.type === 'radio' && field.name) {
var group = document.getElementsByName(field.name);
if (group.length > 0) {
for (var i = 0; i < group.length; i++) {
// Only check fields in current form
if (group[i].form !== field.name) continue;
group[i].classList.remove('error');
}
field = group[group.length - 1];
}
}
// Get field id or name
var id = field.id || field.name;
if (!id) return;
// Check if an error message is in the DOM
var message = field.form.querySelector('.error-message#error-for-' + id + '');
if (!message) return;
// If so, hide it
message.innerHTML = '';
message.style.display = 'none';
message.style.visibility = 'hidden';
};
// Listen to all blur events
document.addEventListener('blur', function (event) {
// Only run if the field is in a form to be validated
if (!event.target.form.classList.contains('validate')) return;
// Validate the field
var error = hasError(event.target);
// If there's an error, show it
if (error) {
showError(event.target, error);
return;
}
// Otherwise, remove any existing error message
removeError(event.target);
}, true);
// Check all fields on submit
document.addEventListener('submit', function (event) {
// Only run on forms flagged for validation
if (!event.target.classList.contains('validate')) return;
// Get all of the form elements
var fields = event.target.elements;
// Validate each field
// Store the first field with an error to a variable so we can bring it into focus later
var error, hasErrors;
for (var i = 0; i < fields.length; i++) {
error = hasError(fields[i]);
if (error) {
showError(fields[i], error);
if (!hasErrors) {
hasErrors = fields[i];
}
}
}
// If there are errrors, don't submit form and focus on first element with error
if (hasErrors) {
event.preventDefault();
hasErrors.focus();
}
// Otherwise, let the form submit normally
// You could also bolt in an Ajax form submit process here
}, false);
Also see: Tab Triggers