Does not contain any HTML when JavaScript is turned off
This means that the URL in question does not contain any content when the JavaScript is turned off.
Why is this important?
The implications of this are far reaching. If a user were to view this page with JavaScript disabled, they would be faced with a blank screen, and screen readers would similarly be unable to access the content, presenting a huge accessibility issue.
This also presents problems from an SEO perspective, as it means that search engines would need to render the content in order to index it. Most search engines still do not do this, and although Google do utilise rendered HTML, even they do not do this as their primary method - they still rely on the source HTML for most of their crawling.
Basic content and page functionality should rely on only the most fundamental web technologies, to ensure that the page is usable across all browsing conditions. Enhanced experiences, such as sophisticated styling using CSS, or interactivity using JavaScript, can be layered on top for the browsers that support those technologies. But basic content and page functionality should not rely on CSS or JavaScript.
What does the Hint check?
This Hint will trigger for any internal HTML URL which does not contain any HTML (literally blank) when JavaScript is turned off. You can easily test this by disabling JavaScipt in your browser, or by emulating it in Chrome DevTools.
How do you resolve this issue?
Progressive Enhancement is a methodology that attempts to deal with this issue, and is built on the concept that you build the main content of web pages from a core foundation of basic technologies, that are accessible across all browsers, and then layer over more advanced functionality using JavaScript and CSS.
How strictly your website adheres to progressive enhancement is a topic of debate, but there's widespread agreement that all pages should display at least some information when JavaScript is disabled, even if the content is just an alert to the user that JavaScript is required to use the page.
For pages that absolutely must rely on JavaScript, one approach is to use a <noscript> element to alert the user that JavaScript is required for the page. This is better than a blank page, because the blank page leaves users uncertain about whether there's a problem with the page, their browsers, or their computers.