🚀 Understanding <!DOCTYPE html> – More Than Just a Line of Code!
Nishi Surti
Have you ever been in an interview where a seemingly simple question caught you off guard? Let's break down one such HTML interview question that can leave developers scratching their heads.
🎤 The Interview Begins
👨💼 Interviewer: What is this <!DOCTYPE html>? Why did you add it?
😨 Scared Developer: Uhh… It tells the browser that my code is using the latest HTML?
😎 Experienced Developer: Actually, <!DOCTYPE html> ensures that my website runs in standard mode instead of quirks mode, following the latest web standards. Without it, my site might behave unpredictably across different browsers.
🤔 But Wait… Is <!DOCTYPE html> Case-Sensitive?
Interviewer (curious and slightly annoyed): Oh! So you want to play? But is it case-sensitive?
🔥 Experienced Developer (smirking): Nope! You can write it as:
<!DOCTYPE html>
<!doctype HTML>
<!DoCtYpE hTmL>
It doesn’t matter. The browser reads it the same way!
💡 Real-World Example – When <!DOCTYPE html> Broke a Website
👨💼 Interviewer (now interested): Give me a real-world example!
💡 Experienced Developer: Sure! The UK government tax website once had a major bug because they forgot to include <!DOCTYPE html>. As a result, their website behaved unexpectedly in older browsers, causing accessibility and layout issues. That’s how critical this small declaration can be!
🔍 How to Check If Your Page is in Standard Mode or Quirks Mode
👨💼 Interviewer (raising the stakes): How can I check which mode my page is using?
🐐 GOAT JavaScript to the rescue:
console.log(document.compatMode);
✅ "CSS1Compat" → Standard Mode (Good!)
❌ "BackCompat" → Quirks Mode (Oops!)
🎯 Lesson of the Day
A great developer doesn’t just write code—they understand why they write it.
📌 Today, we left the Scared Developer Group and leveled up to Experienced Developer Mode! 🚀
🔖 #Day1 of becoming a better developer
💬 What’s an interview question that caught you off guard? Let’s discuss in the comments!
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Written by
Nishi Surti
Nishi Surti
Just a common developer like you ! Let's learn together and lift up each other.