index.js

const BN = require('bignumber.js')

function parseUnit (unit) {
  const decimalsToUnit = {
    '-18': 'wei',
    '-15': 'kwei',
    '-12': 'mwei',
    '-9': 'gwei',
    '-6': 'szabo',
    '-3': 'finney',
    1: 'ether',
    3: 'kether',
    6: 'mether',
    9: 'gether',
    12: 'tether'
  }
  if (typeof unit === 'string') {
    unit = unit.trim().toLowerCase()
  }
  if (unit !== undefined && !isNaN(unit)) {
    unit = decimalsToUnit[unit]
  }
  return unit
}

function convertToEther (value, unit) {
  if (value === undefined) {
    throw TypeError('value is required')
  }
  unit = parseUnit(unit)
  if (unit === undefined) {
    throw TypeError('unit is required')
  }

  const v = new BN(value)
  if (unit === 'eth') unit = 'ether'

  if (unit === 'wei') return v.times(new BN(0.000000000000000001))
  if (unit === 'kwei') return v.times(new BN(0.000000000000001))
  if (unit === 'mwei') return v.times(new BN(0.000000000001))
  if (unit === 'gwei') return v.times(new BN(0.000000001))
  if (unit === 'szabo') return v.times(new BN(0.000001))
  if (unit === 'finney') return v.times(new BN(0.001))
  if (unit === 'ether') return v.times(new BN(1))
  if (unit === 'kether') return v.times(new BN(1000))
  if (unit === 'mether') return v.times(new BN(1000000))
  if (unit === 'gether') return v.times(new BN(1000000000))
  if (unit === 'tether') return v.times(new BN(1000000000000))

  throw TypeError('Invalid unit')
}

function converter (value, unit, toUnit) {
  unit = parseUnit(unit)
  toUnit = parseUnit(toUnit)
  const v = convertToEther(value, unit)
  if (unit === 'eth') unit = 'ether'
  if (toUnit === 'eth') toUnit = 'ether'

  const result = {
    wei: null,
    kwei: null,
    mwei: null,
    gwei: null,
    szabo: null,
    finney: null,
    ether: null,
    kether: null,
    mether: null,
    gether: null,
    tether: null
  }

  result[unit] = new BN(value).toString(10)

  if (unit !== 'wei') { result.wei = v.times(new BN(1000000000000000000)).toString(10) }
  if (unit !== 'kwei') { result.kwei = v.times(new BN(1000000000000000)).toString(10) }
  if (unit !== 'mwei') { result.mwei = v.times(new BN(1000000000000)).toString(10) }
  if (unit !== 'gwei') { result.gwei = v.times(new BN(1000000000)).toString(10) }
  if (unit !== 'szabo') { result.szabo = v.times(new BN(1000000)).toString(10) }
  if (unit !== 'finney') { result.finney = v.times(new BN(1000)).toString(10) }
  if (unit !== 'ether') { result.ether = v.times(new BN(1)).toString(10) }
  if (unit !== 'kether') { result.kether = v.times(new BN(0.001)).toString(10) }
  if (unit !== 'mether') { result.mether = v.times(new BN(0.000001)).toString(10) }
  if (unit !== 'gether') { result.gether = v.times(new BN(0.000000001)).toString(10) }
  if (unit !== 'tether') { result.tether = v.times(new BN(0.000000000001)).toString(10) }

  if (toUnit) {
    if (result[toUnit] === undefined) {
      throw TypeError('Invalid unit')
    }

    return result[toUnit]
  }

  return result
}

module.exports = converter