reference.js

export const definitions = {
  length: { metre: 1, kilometre: 1000, mile: 1609.344, inch: 0.0254, centimetre: 0.01, foot: 0.3048 },
  mass: { kilogram: 1, pound: 0.45359237, ounce: 0.028349523125, gram: 0.001 },
  speed: { metre_per_second: 1, kilometre_per_hour: 1 / 3.6, mile_per_hour: 0.44704, knot: 1852 / 3600 },
  pressure: { pascal: 1, kilopascal: 1000, megapascal: 1000000, bar: 100000, psi: 6894.757293168, atmosphere: 101325 },
  volume: { cubic_metre: 1, litre: 0.001, millilitre: 0.000001, us_liquid_gallon: 0.003785411784, us_fluid_ounce: 0.0000295735295625 },
  energy: { joule: 1, calorie: 4.184, kilowatt_hour: 3600000 },
  data_storage: { byte: 1, megabyte: 1000000, mebibyte: 1048576, gigabyte: 1000000000 },
  time: { second: 1, hour: 3600, day: 86400, week: 604800 },
  angle: { radian: 1, degree: Math.PI / 180 },
  area: { square_metre: 1, acre: 4046.8564224 },
  force: { newton: 1, pound_force: 4.4482216152605 },
  power: { watt: 1, mechanical_horsepower: 745.699871582 }
};

function temperatureToKelvin(value, unit) {
  if (unit === 'kelvin') return value;
  if (unit === 'celsius') return value + 273.15;
  if (unit === 'fahrenheit') return (value + 459.67) * 5 / 9;
  throw new RangeError(`Unknown temperature unit: ${unit}`);
}

function temperatureFromKelvin(value, unit) {
  if (unit === 'kelvin') return value;
  if (unit === 'celsius') return value - 273.15;
  if (unit === 'fahrenheit') return value * 9 / 5 - 459.67;
  throw new RangeError(`Unknown temperature unit: ${unit}`);
}

export function convert(value, category, sourceUnit, targetUnit) {
  if (!Number.isFinite(value)) throw new TypeError('value must be finite');
  if (category === 'temperature') return temperatureFromKelvin(temperatureToKelvin(value, sourceUnit), targetUnit);
  const categoryDefinitions = definitions[category];
  if (!categoryDefinitions) throw new RangeError(`Unknown category: ${category}`);
  const sourceFactor = categoryDefinitions[sourceUnit];
  const targetFactor = categoryDefinitions[targetUnit];
  if (!Number.isFinite(sourceFactor) || !Number.isFinite(targetFactor)) throw new RangeError('Unknown unit');
  return value * sourceFactor / targetFactor;
}