parse-strange-unit.js

let unit = `5" x 5' x 1-3/16"`

unit.split('x')
  .map((v) => v.trim())
  .map((v) => ({ value: removeUnit(v), unit: getUnit(v) }))
  .map(({ unit, value }) => ({ unit, value: value.split('-') }))
  .map(({ unit, value: [whole, fraction] }) => ({ unit, whole, fraction: splitFraction(fraction) }))
  .map(({ unit, whole, fraction }) => ({ unit, value: parseInt(whole) + divideTuple(fraction) }))
  .map(o => convertToInch(o))
  .reduce((product, o) => product * o.value, 1)

let getUnit = (v: string) => v.includes('"') ? 'inch' : v.includes(`'`) ? 'feet' : undefined
let removeUnit = (v: string) => v.replace(/['"]/g, '')
let splitFraction = (v: string = '0/1') => v.split('/') as [string, string]
let divideTuple = ([numerator = '0', denominator = '1'] = ['0', '1']) => parseInt(numerator) / parseInt(denominator)
let convertToInch = (o: { unit: string, value: number }) => o.unit === 'inch' ? o : ({ unit: 'inch', value: o.value * 12 })