Avoiding deprecated tags in HTML - Performance & Optimization

Performance: Avoiding deprecated tags

MEDIUM IMPACT

Using deprecated HTML tags affects browser rendering consistency and can cause layout shifts and slower page load times.

Creating a visually centered heading

HTML

<h1 style="text-align: center;">Welcome</h1>

Using CSS for centering avoids deprecated tags and provides stable, efficient rendering.

📈 Performance GainSingle reflow with stable layout, reducing CLS

Creating a visually centered heading

HTML

<center><h1>Welcome</h1></center>

The <center> tag is deprecated and causes browsers to trigger layout recalculations and inconsistent styling.

📉 Performance CostTriggers multiple reflows and increases CLS due to unstable layout shifts

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Using <center> tag	Adds extra DOM nodes	Multiple reflows due to layout shifts	Higher paint cost from unstable layout	[X] Bad
Using CSS text-align:center	No extra DOM nodes	Single reflow on style application	Lower paint cost with stable layout	[OK] Good

Rendering Pipeline

Deprecated tags cause browsers to fallback on legacy rendering behaviors, triggering extra layout recalculations and paint operations.

→Style Calculation

→Layout

→Paint

⚠️ BottleneckLayout

Core Web Vital Affected

CLS

Using deprecated HTML tags affects browser rendering consistency and can cause layout shifts and slower page load times.

Optimization Tips

1Never use deprecated HTML tags; replace them with semantic tags and CSS.

2Use CSS for all styling and layout control to avoid layout thrashing.

3Check for layout shifts in DevTools to catch deprecated tag issues.

Performance Quiz - 3 Questions

Why should you avoid using deprecated HTML tags like <center>?

A They improve browser compatibility with old devices.

B They cause layout shifts and multiple reflows, hurting visual stability.

C They reduce the file size of HTML documents.

D They speed up CSS parsing.

DevTools: Performance

How to check: Record a performance profile while loading the page and look for layout shifts and reflows caused by deprecated tags.

What to look for: Look for multiple Layout events and high Cumulative Layout Shift (CLS) scores indicating unstable layout.