Execute an asynchronous function in Javascript, then output the returned data to the console

Question

Execute an asynchronous function in Javascript, then output the returned data to the console

Is there a way to effectively handle the data returned from 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 one get complete access to all the information in the JSON file and manipulate it accordingly? For instance, extracting "First" and "Second" and appending them to a div. How about "FirstA" and "FirstB", "SecondA" and "SecondB"... and so forth?

Currently, Promise {: undefined} is what I am getting.

Any assistance on this matter would be highly appreciated.

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

While running the console log within the function reveals the json data, the challenge is accessing the data externally.

Serge

javascript json function asynchronous return

Answer 1

Answer №1

There are two key points to consider:

In order to set the resolution value of the promise generated by the async function, you need to include a return statement within the actual async function and not just within a callback such as getJSON.
To synchronize with and obtain the resolution value of an async function, you must either use await or consume its promise using methods like then.

For point #1, you can modify your code to 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');
    }
}

Regarding point #2, you can either utilize await when handling the function directly or use then when consuming the promise:

console.log(await getData());

...or alternatively use then:

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

Furthermore, it's crucial to note that your current implementation of getData masks errors by transforming them into resolutions with the value of undefined. To avoid this behavior, ensure that errors are properly propagated:

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

Make sure that any code utilizing getData effectively handles or propagates errors to prevent "unhandled rejection" errors.

In response to your query about accessing the content from the JSON file outside the function:

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

The resolved value of getData is the object defined in the JSON file (after parsing). Therefore, you can simply use .stuff to access it:

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

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

Answer 2

There are two key points to consider:

In order to set the resolution value of the promise generated by the async function, you need to include a return statement within the actual async function and not just within a callback such as getJSON.
To synchronize with and obtain the resolution value of an async function, you must either use await or consume its promise using methods like then.

For point #1, you can modify your code to 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');
    }
}

Regarding point #2, you can either utilize await when handling the function directly or use then when consuming the promise:

console.log(await getData());

...or alternatively use then:

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

Furthermore, it's crucial to note that your current implementation of getData masks errors by transforming them into resolutions with the value of undefined. To avoid this behavior, ensure that errors are properly propagated:

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

Make sure that any code utilizing getData effectively handles or propagates errors to prevent "unhandled rejection" errors.

In response to your query about accessing the content from the JSON file outside the function:

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

The resolved value of getData is the object defined in the JSON file (after parsing). Therefore, you can simply use .stuff to access it:

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

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

Answer 3

Answer №2

This is the method I often use. First, create an async function like this:

private logToConsoleAsync = async (message: string, data?: any) => {
    await new Promise((resolve) => setTimeout(resolve, 0)).then(() => console.info(message, data));
};

Then, simply call this function within your own async function when you need to log something:

await this.logToConsoleAsync('This is my message', myData);

Answer 4

This is the method I often use. First, create an async function like this:

private logToConsoleAsync = async (message: string, data?: any) => {
    await new Promise((resolve) => setTimeout(resolve, 0)).then(() => console.info(message, data));
};

Then, simply call this function within your own async function when you need to log something:

await this.logToConsoleAsync('This is my message', myData);

Execute an asynchronous function in Javascript, then output the returned data to the console

Answer №1

Answer №2

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