amount.js

const rdot = /\.(\d*)$/
const rleadzero =  /^0+/

function toIntStr(number) {
  let string = number.toString()
  let exponent = 0
  
  string = string
    .replace(rdot, (str, p) => {
      exponent = p.length
      return p
    })
    .replace(rleadzero, '')
    
  return {
    string,
    exponent
  }
}

function toFloatStr(string, exponent) {
  if (exponent) {
    let length = string.length
    if (exponent < length) {
      string = string.substr(0, length - exponent) + '.' + string.substr(length - exponent)
    }
    else {
      string = '0.' + Array(exponent - length + 1).join('0') + string
    }
  }
  return string
}

export const yuan2fen = function yuan2fen(amount) {
  let symbol = amount < 0 ? -1 : 1
  let result = toIntStr(amount * symbol)
  let fen = toFloatStr(result.string + '00', result.exponent)
  return Number(fen) * symbol
}

export const fen2yuan = function yuan2fen(amount) {
  let symbol = amount < 0 ? -1 : 1
  let result = toIntStr(amount * symbol)
  let yuan = toFloatStr(result.string, result.exponent + 2)
  return Number(yuan) * symbol
}