Unit conversion seems like a solved problem. Multiply by some factor, done. But building a good converter UI taught me a few things.
What Makes It Tricky
- Bidirectional input — both fields need to be editable and stay in sync
- Floating point — 0.1 + 0.2 !== 0.3 in JavaScript. Rounding matters.
- Category switching — length, weight, temperature all have different conversion logic
- Temperature is special — it's not a simple multiply. Celsius to Fahrenheit is
(C * 9/5) + 32
The State Problem
Most beginners store two values and try to keep them synced. That leads to infinite loops. The trick: store ONE source of truth (the value in a base unit) and derive both displayed values from it.
My Unit Converter
I built a converter that handles length, weight, temperature, speed, and data storage. It does bidirectional input, instant conversion, and handles the edge cases gracefully.
Try it: Unit Converter
Takeaway
Simple-seeming projects often hide real engineering problems. That's what makes them great learning tools.