删除字符串中的所有相邻重复项

// 输入："abbaca"
// 输出："ca"
var removeDuplicates = function (str) {
  let stack = []
  for (const s of str) {
    let pre = stack.pop()
    if (pre !== s) {
      stack.push(pre)
      stack.push(s)
    }
  }
  return stack.join('')
}
console.log(removeDuplicates('abbaca'))