HTML Guide

The <script> tag allows authors to include dynamic scripts and data blocks in their documents. When the src is present, this tag accepts a type attribute which must be either:

• an empty string
• text/javascript (that’s the default, so it can be omitted)
• module

Examples:

<!-- This is valid, without a type it defaults to JavaScript -->

<script src="app.js"></script>

<!-- This is valid, but will warn that it can be omitted -->

<script type="text/javascript" src="app.js"></script>

<!-- An empty attribute is valid, but will warn that it can be omitted -->

<script type="" src="app.js"></script>

<!-- The module keyword is also valid as a type -->

<script type="module" src="app.js"></script>

<!-- Any other type is invalid -->

<script type="wrong" src="app.js"></script>
<script type="text/html" src="app.js"></script>
<script type="image/jpeg" src="app.js"></script>

The value rocketlazyloadscript used in a <script> tag is not a valid one according to the HTML specification. It is introduced by the WP Rocket Wordpress extension.

The specified type for an script element is not a valid MIME type as it’s missing a subtype.

A MIME type most-commonly consists of just two parts: a type and a subtype, separated by a slash (/) — with no whitespace between, for example:

text/javascript

The defer and async boolean attributes of the <script> element control how an external script should be executed once it has been downloaded. These attributes only make sense when referring to external scripts, so a src attribute must also be present to specify the location of the script.

Example:

<script defer src="app.js"></script>

If your script is not external, and is inlined within the HTML document, then you should remove the defer attribute, like in this example:

<script>
  console.log("hello");
</script>

The default type for <script> tags is JavaScript, so you don’t need to include the type for JS resources.

A <source> element inside a <picture> that is followed by another <source> or an <img> with srcset must include a media and/or type attribute.

The <source> element is used inside <picture> for responsive images, allowing different resources to be loaded based on conditions such as viewport width (media) or image format (type). According to the HTML standard, when multiple <source> elements are present (or a following <img> with srcset), each <source> must provide a media and/or type attribute so the browser can choose the appropriate resource based on those hints.

Without media or type, the browser cannot distinguish when to use each source, which can lead to validation errors and unexpected rendering behavior.

Incorrect example (causes the validator error):

<picture>
  <source srcset="image1.webp">
  <source srcset="image2.jpg">
  <img alt="" src="fallback.jpg" srcset="fallback2x.jpg 2x">
</picture>

Correct examples (fixing the error):

<picture>
  <source srcset="image1.webp" type="image/webp">
  <source srcset="image2.jpg" type="image/jpeg">
  <img alt="" src="fallback.jpg" srcset="fallback2x.jpg 2x">
</picture>

or

<picture>
  <source srcset="image-small.jpg" media="(max-width: 600px)">
  <source srcset="image-large.jpg" media="(min-width: 601px)">
  <img alt="" src="fallback.jpg" srcset="fallback2x.jpg 2x">
</picture>

By specifying the media and/or type attributes for each <source>, you satisfy the HTML standard and resolve the W3C validator issue.

The <textarea> element does not have a type attribute.

The HTML <textarea> element represents a multi-line plain-text editing control, and is useful when you want to allow users to enter a sizeable amount of free-form text, for example a comment on a review or feedback form.

The type dob is not valid for an input. If you want to build a date picker field, you can use the native HTML input elements with type date, datetime-local, or a generic text input decorated with JavaScript and CSS.

In HTML, the type attribute for the <input> element specifies the type of input control that is to be displayed. The type attribute can have values like text, password, email, date, etc. Using an unsupported or invalid value like dob (which presumably stands for “date of birth”) will cause this validation error.

Here’s an example of how you can correct this issue by using a supported type attribute value for the date of birth input:

<label for="dob">Date of Birth:</label>
<input type="date" id="dob" name="dob">

In this corrected example, we’ve used the type="date" attribute value for the date of birth input. This is a valid type for handling dates in HTML forms. Replace the input type with a supported type according to the specific data you need to capture.

Alternatively you can use a JavaScript library to build a date picker on a generic text input. For example, the popular bootstrap-datepicker library will generate a date picker around a text input.

The type attribute value for the <link> element must be a valid MIME type, such as image/png, not favicon.

The type attribute in a <link rel="icon"> specifies the MIME type of the linked resource. MIME types must follow the standard format, such as image/png for PNG images or image/x-icon for .ico files. Using favicon is incorrect because it is not a registered MIME type, leading to validation errors.

Correct usage for linking a PNG favicon:

<link rel="icon" href="img/favicon.png" type="image/png">

Correct usage for linking an ICO favicon:

<link rel="icon" href="img/favicon.ico" type="image/x-icon">

The type attribute is optional when the server sends the correct Content-Type HTTP header, but it can be included for explicitness and clarity.

Ensure the src attribute on the script element is non-empty and points to a valid resource.

The src attribute in a script element specifies the URL of an external script file. An empty src attribute is invalid because it tells the browser to fetch a resource from a URL that is not provided, leading to loading errors. Instead, ensure that the src attribute contains a valid file path or URL to an existing script file. If the script content is meant to be inline, you should omit the src attribute altogether and include the script content directly within the script element.

Example of a Valid External Script

Here is a valid example of a script element with a non-empty src attribute:

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Valid Script Example</title>
</head>
<body>
  <script src="path/to/script.js"></script>
</body>
</html>

Example of a Valid Inline Script

If the script is to be written inline, exclude the src attribute and write the JavaScript code directly within the script tags:

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Inline Script Example</title>
</head>
<body>
  <script>
    console.log('This is an inline script.');
  </script>
</body>
</html>

Troubleshooting

Double-check the script’s file path:

• Ensure the file path you provide in the src is correct relative to the HTML file.
• Make sure the script file exists in the location specified.
• If using a network URL, verify that the URL is correct and accessible.