Javascript 环回findOne无法正确搜索MongoDB

当我使用findOne搜索MongoDB以查找bookid==readHistory.bookid的对象时。 然而，终端显示：

 Chapter.getContentByHistory = function (userid, bookid, cb) {
    var app = Chapter.app;
    var returnData = {};
    app.models.user.findById(userid, {}, function (err, res) {
      if (err) {
        cb(null, {
          code: -1,
          errMsg: "Cannot find user`s information",
        });
      } else {
        let currentNum = 1;
        const readHistory = res.myBooks.filter(
          (item) => item.bookid === bookid
        )[0];
        console.log("readHistory.bookid == ",readHistory.bookid);
        if (readHistory) currentNum = Math.max(1, +readHistory.hasRead);
        app.models.chapter.findOne ({bookid : readHistory.bookid}, function(err, dos) {
          if (err) {
            console.log("Cannot find content", err);
            cb(null, {
              code : -2,
              errMsg : "Cannot find content"
            });
          }
          else {
            console.log("Find content successfully");
            console.log("content.bookid == ",dos.bookid);
            cb(null, {
              code: 0,
              num: currentNum,
              content: dos.content,
            });
          }
        });
      }
    });
  };

findOne已成功搜索我的MongoDB，但结果的bookid不等于readHistory.bookid。我无法成功找到readHistory.bookid

readHistory.bookid ==  60934ca587014710a4ffbba9
Find content successfully
content.bookid ==  60934ca587014710a4ffbba0