超过18位长度的bigint转进制

用到了bignumber这个库，https://github.com/MikeMcl/bignumber.js
代码：

const BigNumber = require('./bignumber.js')

function string10to36(number) {
  if(number==null)
    return '';

  let n = new BigNumber(String(number));
  return n.toString(36);
}

function string36to10(number_code) {
  let n = new BigNumber(number_code,36);
  return n.toString();
}



  //测试，没问题
    var id = "1382253560489709568";
    var id36 = util.string10to36(id);
    var id10 = util.string36to10(id36);
    console.log(`id=${id},id36=${id36},id10=${id10},${id===id10?'Right':'Wrong'}`);
    //结果id=1382253560489709568,id64=ai27zrfm8ohs,id10=1382253560489709568,Right