Web Features That May Not Work As You'd Expect

Modern web technologies offer increasingly rich online experiences, but some features may behave unexpectedly due to usability, security, and privacy considerations. This article highlights several such instances.

Styling :visited Links and getComputedStyle Limitations

The styling of visited links (<visited></visited>) has long been restricted to prevent history leaks. Attempts to use getComputedStyle on a visited link will return the unvisited style instead. Workarounds using side effects or sibling selectors are ineffective. This limitation underscores the complexities of browser feature exploitation and the need for developers to be aware of these nuances.

Cross-Site Asset Caching Restrictions

Previously, CDNs enabled browser caching of assets like Google Fonts across multiple sites. However, this created significant privacy vulnerabilities, allowing timing attacks to reveal user browsing history. To address this, browsers no longer allow cross-site asset caching.

Inaccuracies in performance.now()

Exploits like Spectre leveraged the high accuracy of performance.now() to access sensitive CPU data. To mitigate this, browsers have intentionally reduced the accuracy of performance.now(), introducing noise (20μs to 1ms) that varies based on factors like HTTP headers and browser settings.

Lazy Loading without JavaScript: A Misconception

While the loading="lazy" attribute simplifies lazy loading for images and iframes (in some browsers), it's crucial to understand that it requires JavaScript to function. Disabling JavaScript prevents lazy loading as an anti-tracking measure. Claims of lazy loading "without JavaScript" are misleading.

User Preference-Based Feature Limitations

Users can significantly restrict browser functionality for enhanced security and privacy, as seen in browsers like Firefox and Tor with "resist fingerprinting" settings. This impacts features like variable precision, API access, and media query matching. Progressive enhancement and graceful degradation are essential to mitigate this.

Screen Reader Semantic Interpretation Inconsistencies

Semantic HTML improves accessibility, but screen readers may not always interpret semantics as expected. Removing list markers can remove semantic meaning in some browsers, and the emphasis conveyed by elements like <strong></strong>, <em></em>, and <mark></mark> might be inconsistent or omitted due to potential noise. Testing with users and considering visual styling are vital.

Non-Persistent Web Storage

Browser vendors may implement expiration policies for web storage to enhance privacy, limiting the persistence of data. Safari, for example, limits script-writable storage to seven days.

Conclusion

Many web features don't behave exactly as intuitively expected. Developers should critically evaluate user needs and prioritize progressive enhancement and graceful degradation to ensure consistent functionality across browsers and user preferences, acknowledging that perfect cross-browser parity is often unattainable. Understanding these limitations is key to building robust and accessible websites.

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