实现一个小的进制转换器...

进制转换

function log(a,b){
  return Math.log(b)/Math.log(a);
}

function convert(_input, source, target) {
  var input = _input.toString();
  var I_L = source.length,T_L = target.length;
  var len = input.length;
  var num = input.split('').reduce((res,letter,i)=>{
    var index = source.indexOf(letter);
    var temp = index * Math.pow(I_L,len - i -1);
    //console.log(`${temp} =  ${index} * (${I_L} ^ ${len -i - 1})`);
    res += temp;
    return res;
  },0);
  
  if(num == 0){
    return target[0];
  }
  var lex = Math.floor(log(T_L,num))+1;
  var _num = num;
//  console.log(`${input} -> ${num}`);
  var res = "";
  
  while( lex > 0 ){
    var Y = Math.pow(T_L,lex-1);
    var temp = Math.floor(_num / Y);
    _num -= Y*temp;
    res += target[temp];
    lex--;
  }
  console.log(res);
  return res;
}