javascript - 代码始终在响应发送到浏览器后执行

Question

这是我遇到的问题，如果我没有在 asyncCall 函数中设置超时，则在异步代码完成之前发送响应，因此我无法从 onlineBooksImages() 函数，但在下面的代码中包含超时

  setTimeout(() => {


    if (onlineBook) {

        res.status(200).render("showBooks",
            {
                result: result,
                favourites: favourites,
                user: user,
                book: onlineBook

            });
    } 



}, 5000);

延迟发送响应，因此我得到了图像，如何编写以下代码以消除超时，该超时比使用异步代码更快的加载时间更长

var boos = []
var boos2 = []
var boos3 = []
var foo = {}
var foo2 = {}
var foo3 = {}

const onlineBook= await Books2.findById(req.params.id);
const Ebook = await Ebooks.findById(req.params.id);

 function onlineBooksImages() {
    return new Promise(resolve => {
        setTimeout(() => {

            let temporaryVar = []
            onlineBook.allimages.forEach(element => {
                gfs.files.findOne({ _id: element }, (err, file) => {
                    if (!file || file.length === 0) {
                        return res.status(404).json({
                            err: "No file exist"
                        });
                    }
                    var u = []
                    u.push(onlineBook._id)
                    var img = []
                    img.push(file)
                    user.push(file)
                    foo3[u] = temporaryVar;
                    //console.log(user.length);
                });
            });
            boos3.push(foo3)

            resolve(boos3);
        }, 100);
    });
} 
  async function asyncCall() {
    console.log('calling');
    if (onlineBook) {
        var result = await onlineBooksImages();
    } else if (Ebook) {
        var result2 = await someOtherFunction();//notImportant

    } else {
        return res.status(404).render('error', { user });
    }
    setTimeout(() => {


        if (onlineBook) {

            res.status(200).render("showBooks",
                {
                    result: result,
                    favourites: favourites,
                    user: user,
                    book: onlineBook

                });
        } 



    }, 5000);

}

Answer 1

在回答之前......这里有一些有趣的代码

  this code looks wrong on many levels

  var u = [];
  u.push(onlineBook._id);
  // snip
  foo3[u] = temporaryVar;

现在，我们说 onlineBook._id === "abc"

因此u === ['abc']

所以 foo3[u] 与 foo3[u.toString()] 相同...这将是 foo3['abc']

那么为什么不只是foo3[onlineBook._id] = temporVar;

但即使这样看起来也很奇怪，因为 foo3 中的每个属性都将引用同一个数组

例如如果图书 ID 为“abc”、“def”和“ghi”，则 foo3.abc、foo3.def 和 foo3.ghi 将是完全相同的空数组!

无论如何，给出一个答案，虽然我仍然对你的“全局”boos* 和 foo* 变量感到困惑 - 但让我们解决你遇到的问题:

function async onlineBooksImages() {
  let temporaryVar = [];
  for (let element of onlineBook.allimages) {
    try {
      const file = await new Promise((resolve, reject) => {
        gfs.files.findOne({_id: element}, (err, file) => {
            if (err) {
                return reject(err);
            }
            temporaryVar.push(file);
            resolve(file);
        })
      });
      if (!file || file.length === 0) {
        return reject();
      }
      foo3[onlineBook._id] = temporaryVar;

    } catch(e) {
        // do nothing but catch the error
    }
  }
  if (Object.keys(foo3).length) {
    boos3.push(foo3);
    return boos3;
  } else {
    // reject if there were no images in any of allimages
    throw({status: 400, err: "No file exist"});
  }
}

async function asyncCall() {
  console.log('calling');
  try {
    if (onlineBook) {
      var result = await onlineBooksImages();
    } else if (Ebook) {
      var result2 = await someOtherFunction();//notImportant
    } else {
      return res.status(404).render('error', { user });
    }
    if (onlineBook) {
      res.status(200).render("showBooks", {
        result: result,
        favourites: favourites,
        user: user,
        book: onlineBook
      });
    } 
  } catch(e) {
      if (e.status && e.err) {
        res.status(e.status).json({
          err: e.err
        });
      }
  }
}