Promise returning to then before resovle

Question

I have books object having data stored in file. I am reading data from each file and creating books.

Here issue is createBooks promise then is getting called before completion of reading file and success of createBook method call.

  createBooks: function (books) {
    return new Promise((resolve, reject) => {
        const booksArray = Object.entries(books);
        const aPromises = [];
        booksArray.forEach(([key, value]) => {          
            if(value.data){
                const oFileReader = new FileReader();
                oFileReader.readFile(value.data)
               .then((product) => {
                aPromises.push(this.Service.createBook(books));
               });
            }
        });
        Promise.all(aPromises)
            .then(results => resolve(results))
            .catch(error => reject());
        });
  },

You're executing `Promise.all` before even pushing the first Promise in the aPromises array. It's executing on an empty array. `readFile` is asynchronous. — Jeremy Thille, May 14 '20 at 08:39
Does this answer your question? [How do I return the response from an asynchronous call?](https://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call) — Jeremy Thille, May 14 '20 at 08:41
You need to push the *whole promise chain* (i.e. starting from `oFileReader.readFile`) into the array. Also note that using `new Promise` is pointless here, you could `return Promise.all` instead. — jonrsharpe, May 14 '20 at 08:41
The FileReader method is called `readAsText()`, and it doesn't return a Promise. Also, you're doing nothing with the returned `product`, instead each Promise is trying to push `this.Service.createBook(books)` into the promise array. — , May 14 '20 at 08:45
@ChrisG `booksArray.map(getFileContent).then` isn't going to work — Lennholm, May 14 '20 at 09:13
@Lennholm True, thanks, code fixed: https://pastebin.com/FpMEEMNT — , May 14 '20 at 09:19
there was a typo .Actually it is oFileReader.readFile(value.data) .then((book) => { aPromises.push(this.Service.createBook(book)); }); — viswa teja, May 14 '20 at 09:23
Your code has more issues than just a typo. Again, there's no `readFile` method, and even if you replace that with an existing one, it still doesn't return a thenable object. — , May 14 '20 at 11:23
@ChrisG In my case readFile method is promise which has code for converting to text ``` var oFileReader = new FileReader(); oFileReader.readFile(data) .then(() => { }); — viswa teja, May 14 '20 at 11:26

score 0 · Answer 1 · answered May 14 '20 at 08:50

Try to log aPromises array values before Promise.all(aPromises). Are there Promise<> objects?

What does the this.Service.createBook(books) return?

FileReader does not have readFile method.

You should use oFileReader.onload handler

oFileReader.onload = function(){
    aPromises.push(this.Service.createBook(books));
};

oFileReader.readAsDataURL(value.data); // value.data - has to be File
// oFileReader.readAsText(value.data); // value.data - has to be blob

Promise returning to then before resovle

1 Answers1