提交时出现这个问题
代码：

/**

• @param {string} s
• @param {string} t
• @return {string}
  */
  var minWindow = function(s, t) {
  if (s.length < t.length) return ''
  if (s === t) return s;
  let l = 0;
  let r = 0;
  let res = ''
  const map = new Map();
  for(let j = 0; j < t.length; j += 1) {
  map.set(t[j], map.get(t[j]) ? map.get(t[j]) + 1 : 1);
  }
  let needType = map.size;
  while(r < s.length) {
  const ele = s[r];
  if (map.has(ele)) {
  map.set(ele, map.get(ele) - 1);
  if (map.get(ele) === 0) {
  needType -= 1;
  }
  }
  while(needType === 0) {
  let leftEle = s[l];
  let res2 = s.substring(l, r + 1);
  if (!res || res2.length < res.length) res = res2;
  console.log(res);
  if (map.has(leftEle)) {
  map.set(leftEle, map.get(leftEle) + 1);
  if (map.get(leftEle) === 1) {
  needType += 1;
  }
  }
  l += 1
  }
  r += 1;
  }
  return res;
  };