Javascript async function console log the returned data

Question

How can I console log - or do any thing with the data returned from inside an async function?

example: JS FILE:

   async function getData(){
      try {
         $.getJSON('./data.json', (data) => {
            return data;
         });
      } catch(error) {
         console.log("error" + error);
      } finally {
         console.log('done');
      }
   }

   console.log(getData());

JSON FILE:

{
   "stuff": {
      "First": {
         "FirstA": {
            "year": [2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017],
            "Categories": ["Suspension", "Electrical", "Performance", "Motor"]
         },
         "FirstB": {
            "year": [2007, 2008, 2009, 2010, 2011, 2012],
            "Categories": ["Suspension", "Electrical", "Performance", "Motor"]
         }
      },
      "Second": {
         "SecondA": {
            "year": [2002, 2003, 2004, 2005, 2006],
            "Categories": ["Suspension", "Electrical", "Performance", "Motor"]
         },
         "SecondB": {
            "year": [2007, 2008, 2009, 2010, 2011, 2012],
            "Categories": ["Suspension", "Electrical", "Performance", "Motor"]
         }
      }
   }
}

How can I return / get access to all the information in the JSON file and work with it. for example I'd like to take the "First" and "Second" and add them to a div. Same with "FirstA" and "FirstB" and "SecondA" and "SecondB"...and so on.

Right now as it stands, I get Promise {: undefined}

Any help would be greatly appreciated.

---------UPDATE---------

If I run the console log inside the function I then can see the json data, but I need access to the data outside the function.

Serge

Solution

Two issues:

1. To set the resolution value of the promise created by the async function, you have to use a return statement from the async function itself. Your code has a return in the getJSON callback (which is ignored), not the async function itself.

2. To get the resolution value of an async function, you must await it (or consume its promise in the older way, via then, etc.).

For #1, you could return the result of awaiting getJSON:

async function getData() {
    try {
        return await $.getJSON('./data.json').promise();
    }
    catch (error) {
        console.log("error" + error);
    }
    finally {
        console.log('done');
    }
}

And for #2, you'd need to either await your function (this would, in turn, need to be inside an asyncfunction):

console.log(await getData());

...or consume its promise via then:

getData().then(data => {
    console.log(data);
});

---

Side note: Your getData hides errors, turning them into resolutions with the value undefined, which is generally not a good idea. Instead, ensure that it propagates the error:

catch (error) {
    console.log("error" + error);
    throw error;
}

Then, naturally, ensure that anything using getData either handles or propagates the error, making sure something somewhere does handle it (otherwise, you get an "unhandled rejection" error).

---

Re your comment

how would I access the "stuff" in the json file from the log outside the function?

The async result / resolution value of getData is the object the JSON defined (it's no longer JSON, it's been parsed). So you'd use .stuff on it, e.g.:

// In an `async` function
console.log((await getData()).stuff);

// Or using `then`:
getData().then(data => {
    console.log(data.stuff);
});

Comments

[Sergio]

T.J. Crowder in the first example what is the "i" in the i.getJSON and where is it coming from? I know I am sprinkling some jQuery in there with the getJSON method, but just testing to see if this would work.

[T.J. Crowder]

@Sergio: It was a typo (now fixed). Which is odd, given that I used copy and paste. So maybe not a typo, but rather an editing error. :-)

[Sergio]

hahaha...it's no biggie. Ok, just tested and now something is happening.

[Sergio]

now how would I access the "stuff" in the json file from the log outside the function? I tried console.log(getData().stuff); and I get undefined.

[T.J. Crowder]

@Sergio: Yes, of course you do, because getData returns a promise, and promises don't have a property called stuff. I've added to the end of the answer.

[Sergio]

Perfect. Thank you for your help. Using the .then method worked for me. the await kept giving me an error of Unexpected identifier

[T.J. Crowder]

@Sergio: No worries. Yes. As I said above, you can only use await in an async function.

[Sergio]

aahh... so the "await" can only be used inside the async function. Outside the async function "then" should be used - as you clearly commented out in your example lol.

[Sergio]

T.J. I have a follow-up question posted here...if you can, can you take a look at it. Thanks. stackoverflow.com/questions/48036910/…

[buncis]

with arrow function you could just do async () => console.log(await getData())