To handle HTML errors, you need to start from four aspects: structural specification, resource loading, form verification and compatibility. 1. Use effective structure to ensure that the tag is closed and the semantics are correct, and avoid misalignment; 2. Add alt attribute to the picture and set an error fallback scheme to monitor the failure of resource loading; 3. Use required and pattern attributes to perform form verification, and at the same time the backend is validated again, combining JS to improve the experience; 4. Use progressive enhancement strategies to provide fallback content, and test the performance of mainstream browsers. Use polyfill to be compatible with the old environment if necessary.
Handling HTML errors does not actually have a clear try-catch mechanism like writing JavaScript, but it does not mean that it is not important. Common errors in HTML pages include unclosed tags, confusing structures, failed reference resources, etc. These problems may cause abnormal page rendering or affect SEO. The following is a few practical perspectives to talk about how to better deal with possible problems in HTML.

Using a valid HTML structure
This is the most basic and easiest point to be overlooked. A well-structured and semantic HTML page can not only improve accessibility, but also reduce the probability of errors in browser parsing.
- Make sure the tags appear in pairs : for example,
<div> should have corresponding <code>
<header></header>
, <main></main>
, <footer></footer>
, etc., which help browsers and auxiliary tools correctly identify content structure.<div> in the <code><p></p>
tag, otherwise <p></p>
may be automatically disconnected in some browsers, causing unexpected behavior.A good way to verify HTML is to use W3C's HTML Validator , throw your page in and run it, and it will tell you where it doesn't comply with the specification.

Handling of failed loading of pictures and external resources
Image path errors and CDN resources are common, especially in the production environment after deployment, it is easy to expose problems.
- Add
alt
attribute to the image : This way, even if the image fails to load, the user can know what the image should display. - Use
onerror
to fall back to the default graph (for inline) :
<img src="/static/imghw/default1.png" data-src="image.jpg" class="lazy" alt="descriptive text" oneerror="this.src='fallback.jpg';">
- CSS background image can be backed up using
background-image
solution , or a default background color/pattern can be set as a guarantee.
In addition, if the monitoring resource fails to load, you can do some log reporting through JS to facilitate subsequent troubleshooting.

Handle common errors in form submissions
Although HTML5 already comes with some form verification functions (such as required
, type="email"
), these are only front-end checks and cannot be completely relied on.
- Add
required
attributes to each input field to avoid missing critical information. - Use
pattern
attribute reasonably for format verification , such as phone number, zip code, etc.:
<input type="text" pattern="\d{6}" title="Please enter the 6-digit zip code">
- The backend must verify the data legitimacy again , because frontend verification can be bypassed.
For more complex scenarios, it is recommended to combine JavaScript to perform custom prompts or asynchronous verification to improve user experience.
Browser compatibility and downgrade strategies
Different browsers have slightly different levels of support for HTML, especially older browsers (such as IE).
- Use progressive enhancement strategies : first ensure basic functions are available, then add advanced features.
- Provide fallback content : for example, use
<noscript></noscript>
to wrap alternative content when there is no JS. - Test the performance of mainstream browsers : Chrome, Firefox, Safari and mobile browsers must all be covered.
Some new features (such as <dialog></dialog>
) are not supported in old browsers. At this time, you can use polyfill or fallback to the general div JS implementation.
Basically that's it. HTML error handling is not something that can be achieved overnight. The key is to develop good coding habits and cooperate with verification tools and actual testing to find problems. Many problems may seem small, but they will affect the overall experience when accumulated.
The above is the detailed content of HTML Error Handling Techniques. For more information, please follow other related articles on the PHP Chinese website!

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