Async/Await + Ajax .done: Returning undefined

Question

Sorry if this is extremely simple, I can't get my head around it. I've seen similar questions but nothing which gets to the heart of my problem, I think. I have a simple async function:

async function isOpen() {

    var open;

    var data = $.ajax({
      //Working code here
    });

    data.done(function(dat) {
        var obj = JSON.parse(dat);
        var msg = "";

        for (var i = 0; i < obj.length; i++) {

            let closingDate = Date.parse(obj[i].close);
            let openingDate = Date.parse(obj[i].open);

            if (closingDate > Date.now() && openingDate < Date.now()) {
                open = true;
            } else {
                open = false;
            }
        }
    });

    return open;
}

I know that this code is all working - using console.log I have seen that open is always successfully assigned to true or false. So I call this async function from another async function:

async function testFunction(){

    const open1 = await isOpen();
    //More code here...

}

But open1 (in testFunction) is always undefined - even though I use await.

Any ideas what this could be?

is open also true or false if you console.log it directly before returning it? And is it still undefined if you set var open = null; at the begining? — db3000, Aug 19 '21 at 11:18
Also, the for loop will overwrite the result of `open`, you may break the loop once your assign a value to open. — ikhvjs, Aug 19 '21 at 11:19
Use `const dat = await data` followed by your code instead of using the `data.done()` callback. (Assuming you use jQuery 3). — 3limin4t0r, Aug 19 '21 at 11:20
Does this answer your question? [How to return the response from an asynchronous call](https://stackoverflow.com/questions/14220321/how-to-return-the-response-from-an-asynchronous-call) — Liam, Aug 19 '21 at 11:28

Bravo · Accepted Answer · 2021-08-19T11:28:39.897

3

async function isOpen() {

    var open;

    var data = await $.ajax({
      //Working code here
    });

    var obj = JSON.parse(data);
    var msg = "";

    for (var i = 0; i < obj.length; i++) {

        let closingDate = Date.parse(obj[i].close);
        let openingDate = Date.parse(obj[i].open);

        if (closingDate > Date.now() && openingDate < Date.now()) {
            open = true;
        } else {
            open = false;
        }
    }
    return open;
}

of course, the value of open will be determined by the last obj[i]

So you want

async function isOpen() {
    const data = await $.ajax({
      //Working code here
    });
    const obj = JSON.parse(data);
    let msg = "";

    for (var i = 0; i < obj.length; i++) {

        const closingDate = Date.parse(obj[i].close);
        const openingDate = Date.parse(obj[i].open);

        if (closingDate > Date.now() && openingDate < Date.now()) {
            return true;
        }
    }
    return false;
}

Or even

async function isOpen() {
    const data = await $.ajax({
      //Working code here
    });

    const obj = JSON.parse(data);
    let msg = "";
    return obj.some(({open, close}) => {
        const closingDate = Date.parse(close);
        const openingDate = Date.parse(open);
        const now = Date.now();
        return closingDate > now && openingDate < now();
    });
}

edited Aug 19 '21 at 11:28

answered Aug 19 '21 at 11:19

Bravo

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`msg` can be removed too. – Ravi K Thapliyal Aug 19 '21 at 11:33
Depending on the `dataType` you wouldn't even need to parse the data if it's set to "JSON". – Andy Aug 19 '21 at 11:34
@RaviKThapliyal - yeah I know - but not going to do everything :p – Bravo Aug 19 '21 at 11:35
@ikhvjs - I doubt anyone uses jquery that old – Bravo Aug 19 '21 at 11:35
@Andy - not my call ... who knows what `//Working code here` even does – Bravo Aug 19 '21 at 11:35
@bravo, it wasn't a comment about your code. I was just pointing something out. – Andy Aug 19 '21 at 11:37
@Bravo Just pointed it out 'cause you removed `open`, thought `msg` could go out too. Great answer nonetheless :) – Ravi K Thapliyal Aug 19 '21 at 13:48
@RaviKThapliyal - I understand, I removed open because I knew what it was there for, no idea why msg is there :p – Bravo Aug 19 '21 at 13:59

Utkarsh Dixit · Answer 2 · 2021-08-19T11:26:35.200

This is happening because you are using a callback for ajax request and not waiting for ajax request to complete, which is going to set open in isOpen. You can return a Promise to resolve this,

function isOpen() {
  return new Promise((resolve, reject) => {
    var open;

    var data = $.ajax({
      //Working code here
    });

    data.done(function(dat) {
        var obj = JSON.parse(dat);
        var msg = "";

        for (var i = 0; i < obj.length; i++) {

            let closingDate = Date.parse(obj[i].close);
            let openingDate = Date.parse(obj[i].open);

            if (closingDate > Date.now() && openingDate < Date.now()) {
                open = true;
            } else {
                open = false;
            }
        }
       resolve(open);
    });

  }
}

Note: For the above code, you need to handle the logic for errors in the callback, using reject otherwise it will hang forever.

Async/Await + Ajax .done: Returning undefined

2 Answers2