leetcode-402.js

var removeKdigits = function(num, k) {
  if (k == num.length) {
    return "0"
  }
  if (k == 0 || num.length == 1) {
    return num
  }
  
  const substr = num.substring(0, num.length - k + 1)
  const minPos = calculateMinPos(substr)
  let nextPos = minPos
  if (num[minPos] === "0") {
    nextPos++
  }
  const comp = num.substring(nextPos + 1)
  const result = num[num[minPos] === 0 ? nextPos : minPos]
  return (result === "0" ? "" : result) + removeKdigits(comp, k - minPos)
};

function calculateMinPos(str) {
  let min = str[0]
  let pos = 0
  for (let i=1; i < str.length; i++) {
    if (str[i] < min) {
      min = str[i]
      pos = i
    }
  }
  return pos
}

No funciona cuando hay 0's intermedios.