winter 大大的前端进阶训练营 第三周 字符串与数字之间的互相转化作业

<!--
 * @Date: 2020-05-26 18:58:36
 * @LastEditors: xuchao
 * @LastEditTime: 2020-05-26 20:52:08
 * @FilePath: /暂时性缓存区/stringToNumber.html
-->

<script>
  function convertStringToNumber(string, radix = 10) {
    // 十进制以上的数不支持 (eg: ABCDFG)
    if (radix > 10) {
      return
    }
    // 字符串里面s是否有 e|E
    let flag = /e|E/.test(string)
    if (!flag) {
      let chars = string.split('')
      let number = 0
      let i = 0
      while (i < chars.length && chars[i] != '.') {
        number = number * radix
        number += chars[i].codePointAt(0) - '0'.codePointAt(0)
        i++
      }
      if (chars[i] === '.') {
        i++
      }
      let fraction = 1
      while (i < chars.length) {
        fraction /= radix
        number += (chars[i].codePointAt(0) - '0'.codePointAt(0)) * fraction
        i++
      }
      return number
    } else {
      let logNumber = Number(string.match(/\d+$/)[0])
      let number = string.match(/^[\d\.]+/)[0].replace(/\./, '')
      if (/e-|E-/.test(string)) {
        return Number(number.padEnd(logNumber + 1, 0))
      } else {
        return Number(
          number.padStart(logNumber + number.length, 0).replace(/^0/, '0.')
        )
      }
    }
  }
  // document.write(convertStringToNumber('3.4556645445E20'))

  function convertNumberToString(number, radix) {
    let integer = Math.floor(number)
    let fraction = String(number).match(/\.\d+$/)
    if (fraction) {
      fraction = fraction[0].replace('.', '')
    }
    let string = ''
    while (integer > 0) {
      string = String(integer % radix) + string
      integer = Math.floor(integer / radix)
    }
    return fraction ? `${string}.${fraction}` : string
  }
  document.write(convertNumberToString('100.00148498', 10))
</script>