如何修复此异步/等待 function？

Question

I am trying to get the number of documents in my mongodb collection using async and await. When I run this piece of code I get "TypeError: cb is not a function".

I have tried using promises to get this to work, however I am still inexperienced with this topic and I am still learning how to work with promises.

Here is the call

  getFlashCard : function(colName, flashID, callback) {

    var docCount = documentCount();

    console.log(docCount);
   }

Here is the function

 async function documentCount() {
     const count = await mongodb.collection("Interview  Questions").count();              
     return count;
   }

I am getting an error that says " cb(err, val) ^

TypeError: cb is not a function at runInAsyncScope "

Answer 1

Actually you dont need async and await for this because its already an promise. Just add an then on the end:

 mongodb.collection("Interview  Questions").count().then(count => {
 console.log("counted: " + count)
 })

Answer 2

documentCount() is an async function. As such, it returns a promise. All async functions return a promise. So, the way you get a value out of a promise is the same as with any promise. You use .then() or await on it. So, in getFlashCard() , you could do something like this:

getFlashCard : function(colName, flashID, callback) {

    documentCount().then(docCount => {
        console.log(docCount);
    }).catch(err => {
        console.error(err);
    });
}

This assumes that you're using your mongodb.collection().count() properly and that it returns a promise. If that's not the case, then you will also have to fix that (I don't personally know mongodb).

FYI, it appears you created documentCount() hoping to turn an asynchronous value into a synchronous value. You can't do that in Javascript. While await suspends execution within a function and lets you appear to write more synchronous looking code for asynchronous operations, it doesn't work across a function boundary. You cannot change an asynchronous value into a synchronous value in Javascript. So, anyone who wants to use the docCount value will have to deal with it asynchronously as I've shown above in getFlashCard() .