Unit Converter: Fahrenheit input bypasses absolute-zero validation and yields negative Kelvin #11103

Summary

public/Unit-Converter/script.js validates below-absolute-zero inputs only when the source unit is Kelvin or Celsius. Selecting Fahrenheit as the source unit skips both guards entirely, so physically impossible temperatures convert successfully into negative Kelvin - contradicting the validation the same form enforces for the other two units.

Static-analysis finding based on reading branch Main; not executed here.

Location

• File: public/Unit-Converter/script.js
• Functions: validateInput() (guards at ~lines 303-325) and convertTemperature() (~lines 349-371)

if(fromUnit.value==="kelvin" && value<0){
  return { valid:false, message:"Temperature cannot be below 0 Kelvin" };
}
if(fromUnit.value==="celsius" && value<-273.15){
  return { valid:false, message:"Temperature cannot be below -273.15 C" };
}

There is no corresponding guard for fromUnit.value==="fahrenheit" (-459.67 F = absolute zero), while convertTemperature() processes any Fahrenheit value ((value-32)*5/9, then +273.15 for Kelvin output).

Trigger / Reproduction

Based on source reading:

1. Category: Temperature, From: Fahrenheit, To: Kelvin.
2. Enter -500 (the input filter allows -).
3. Validation passes (no Fahrenheit branch).
4. Output: (-500-32)*5/9 + 273.15 = -22.41 K.

Expected Behavior

The same physical state must be rejected regardless of source unit: entering -22 K directly shows "Temperature cannot be below 0 Kelvin", so converting to that identical value from Fahrenheit should be rejected too.

Actual Behavior

A negative Kelvin result is displayed as a successful conversion.

Impact

The converter's core purpose (physically valid conversions) silently breaks for one of its three supported units; users receive impossible values with no warning.

Suggested Direction

Convert the input to Kelvin first inside validateInput() (or add the missing Fahrenheit guard < -459.67) so the physical limit is enforced once for all units instead of per-unit in the input scale.

I'd like to take this up - requesting assignment per GSSoC'26 first-come-first-serve guidelines (@Poojax21).