js实现无限操作

function add(x, y) {
  if (isNaN(+x)) {
    x = 0;
  } 
  if (isNaN(+y)) {
    y = 0;
  }
  return x + y;
}
var operator = (function(op) {
  let result = null;
  return function (x) {
    if (x) {
      result = op(x, result);
      return arguments.callee;
    } else {
      let ret = result;
      result = null;
      return ret;
    }
  }
})(add);