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.

Practice

1. Which of the following tags is deprecated and should be avoided in modern HTML?

easy

A. <article>

B. <center>

C. <section>

D. <nav>

Solution

1. Step 1: Understand deprecated tags

   The <center> tag was used to center content but is now deprecated in favor of CSS styling.

2. Step 2: Identify semantic tags

   <section>, <article>, and <nav> are semantic HTML5 tags and are not deprecated.

3. Final Answer:

   <center> -> Option B

4. Quick Check:

   Deprecated tag = <center> [OK]

Hint: Deprecated tags are old layout tags replaced by CSS [OK]

Common Mistakes:

• Confusing semantic tags with deprecated tags
• Thinking all tags with angle brackets are deprecated
• Assuming <b> is semantic

2. Which is the correct modern way to make text bold instead of using the deprecated <b> tag?

easy

A. <i>Text</i>

B. <bold>Text</bold>

C. <em>Text</em>

D. <strong>Text</strong>

Solution

1. Step 1: Identify semantic bold tag

   The <strong> tag is the semantic way to indicate important or bold text.

2. Step 2: Recognize deprecated and incorrect tags

   <b> is deprecated for styling; <bold> is invalid; <em> and <i> are for emphasis and italic style, not bold.

3. Final Answer:

   <strong>Text</strong> -> Option D

4. Quick Check:

   Use <strong> for bold text [OK]

Hint: Use semantic tags like strong for bold, not <b> [OK]

Common Mistakes:

• Using <b> for styling instead of <strong>
• Confusing <em> with bold
• Using invalid tags like <bold>

3. What will the following HTML code render in a modern browser?

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

medium

A. The heading 'Welcome' centered horizontally

B. The heading 'Welcome' left aligned (default)

C. A syntax error, page won't load

D. The heading 'Welcome' in italic style

Solution

1. Step 1: Recognize deprecated tag behavior

   Although the <center> tag is deprecated in HTML5, modern browsers continue to support it for backward compatibility and will center the content.

2. Step 2: Default heading alignment

   The <h1> inside <center> will be rendered centered horizontally.

3. Final Answer:

   The heading 'Welcome' centered horizontally -> Option A

4. Quick Check:

   Deprecated <center> still centers [OK]

Hint: Deprecated tags like <center> still render their effect in modern browsers [OK]

Common Mistakes:

• Thinking deprecated tags are completely ignored
• Believing deprecated tags cause syntax errors
• Confusing <center> with italic or bold

4. Identify the error in this HTML snippet and choose the best fix:

<font color='red'>Warning!</font>

medium

A. Replace <font> with <span> and use CSS color

B. Keep <font> but add style attribute

C. Change color attribute to text-color

D. Use <b> instead of <font>

Solution

1. Step 1: Recognize deprecated tag usage

   The <font> tag is deprecated and should not be used for styling.

2. Step 2: Use semantic tag with CSS

   Use a <span> tag and apply color with CSS, e.g., style="color:red;".

3. Final Answer:

   Replace <font> with <span> and use CSS color -> Option A

4. Quick Check:

   Use CSS for styling, not <font> [OK]

Hint: Use <span> + CSS instead of deprecated <font> [OK]

Common Mistakes:

• Trying to fix <font> with invalid attributes
• Using <b> for color styling
• Ignoring CSS for styling

5. You want to center a paragraph and make its text italic without using deprecated tags. Which is the best modern HTML and CSS approach?

hard

A. <center><i>Text</i></center>

B. <p><font align='center'><i>Text</i></font></p>

C. <p style='text-align:center; font-style:italic;'>Text</p>

D. <p><b><em>Text</em></b></p>

Solution

1. Step 1: Avoid deprecated tags

   <center> and <font> are deprecated and should not be used.

2. Step 2: Use CSS for styling

   Apply text-align:center; and font-style:italic; using the style attribute or external CSS on a semantic tag like <p>.

3. Final Answer:

   <p style='text-align:center; font-style:italic;'>Text</p> -> Option C

4. Quick Check:

   Use CSS styles, not deprecated tags [OK]

Hint: Use CSS styles on semantic tags, never deprecated tags [OK]

Common Mistakes:

• Using <center> or <font> for layout and style
• Mixing bold and italic tags incorrectly
• Not applying CSS for alignment or style