Write a function that can do the 4 basic operations (add, subtract, multiply and divide) on two fractions. Return the most simplified form of the result.

fractionMath.ts

type FractionString = `${number}/${number}`
type Fraction = { numerator: number; denominator: number }
type Operation = 'add' | 'subtract' | 'multiply' | 'divide'

const simplify = ({ numerator, denominator }: Fraction) => {
  const commonDivisor = (n: number, d: number) => (d === 0 ? n : commonDivisor(d, n % d))
  const divisor = commonDivisor(numerator, denominator)
  return { numerator: numerator / divisor, denominator: denominator / divisor }
}

const getFraction = (fraction: FractionString) => {
  const [numerator, denominator] = fraction.split('/').map(Number)
  return { numerator, denominator }
}

const operate: Record<Operation, (f1: Fraction, f2: Fraction) => Fraction> = {
  add: ({ numerator: n1, denominator: d1 }, { numerator: n2, denominator: d2 }) => ({ numerator: n1 * d2 + n2 * d1, denominator: d1 * d2 }),
  subtract: ({ numerator: n1, denominator: d1 }, { numerator: n2, denominator: d2 }) => ({ numerator: n1 * d2 - n2 * d1, denominator: d1 * d2 }),
  multiply: ({ numerator: n1, denominator: d1 }, { numerator: n2, denominator: d2 }) => ({ numerator: n1 * n2, denominator: d1 * d2 }),
  divide: ({ numerator: n1, denominator: d1 }, { numerator: n2, denominator: d2 }) => ({ numerator: n1 * d2, denominator: d1 * n2 }),
}

const fractionMath = (f1: FractionString, op: Operation, f2: FractionString) => {
  const result = simplify(operate[op](getFraction(f1), getFraction(f2)))
  return `${result.numerator}/${result.denominator}`
}