document.querySelector() vs. getElementById(): Which is Faster?

When selecting DOM elements in JavaScript, two common methods are document.querySelector() and document.getElementById(). But which one is faster and when should you use each? Let’s break it down. See Memory Management in JavaScript.

1. Speed Comparison 🚀

Benchmark tests consistently show that:
✅ getElementById() is faster than querySelector().

Why?

• getElementById() directly accesses the DOM’s optimized ID lookup system.
• querySelector() uses a CSS selector engine, which adds slight overhead.

Performance Test Example

console.time('getElementById');
for (let i = 0; i < 10000; i++) {
  document.getElementById('test');
}
console.timeEnd('getElementById'); // ~1-5ms

console.time('querySelector');
for (let i = 0; i < 10000; i++) {
  document.querySelector('#test');
}
console.timeEnd('querySelector'); // ~5-15ms

Result: getElementById() is 2-10x faster in most cases.

2. When to Use Each?

✅ Use getElementById() When:

• You only need to select one element by ID.
• Performance is critical (e.g., in loops or animations).

✅ Use querySelector() When:

• You need complex CSS selectors (e.g., .class, [attribute], parent > child).
• You want a single method for all selections (IDs, classes, etc.).

3. Key Takeaways

Final Verdict

• If speed matters, use getElementById().
• If flexibility matters, use querySelector().

Pro Tip: For modern JS, getElementById() is still king for pure performance—but querySelector() is more versatile.

Which do you prefer? 🚀

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