Ndtyjky

Can you help me understand why this doesn't work:

I'm working in Aurelia, and I try to validate some input data using the validation controller, which is documented here: https://aurelia.io/docs/plugins/validation#validation-controller

Now, I have a map of this data, where I need to evaluate each entry, and I want to create an array, where each item contains the validation result of each entry, and when everything is done, return the array.

So something like this (simplified):

function ValidateAll(InputDataMap){

  let validationResults = new Array();



  InputDataMap.forEach((item) => {

     validationResults.push(validateEntry(item));

  });



 return validationResults;

}



function validateEntry(item){



(aurelia's validation)controller.validate(item, "some value", "some rule")

      .then(result => {

        return result;

      });

}

Now, this will not work of course, because I need to wait for the validation controller to resolve it's promise before I can get any data back, and so far I've failed at that.

I read that if you use the async/await keyword it will pause a function until the promise has been resolved, so I made changes, something like this:

function ValidateAll(InputDataMap){

      let validationResults = new Array();



      InputDataMap.forEach(async(item) => {



         let result = await validateEntry(item);

         validationResults.push(result);

});

Now, this doesn't work either, and that's what I'm wondering about. I suppose that my "validateEntry" function is considered finished by the "await" once it's run, and doesn't wait for the "validate()" function's promise inside "validateEntry" to be resolved. Can I write it as simply as this with a few modifications and still get it to work?

You have to return a Promise from your validateEntry:

function validateEntry(item){

  return controller.validate(item, "some value", "some rule")

}

A then just returning its parameter is not required, and does nothing, so .then(result => { return result; }) can be removed.

The async callback for the forEach would not make ValidateAll to wait for the validation. You have to wait for all Promises to be resolved, and return a Promise from ValidateAll, the forEach can be replaced by map so that you don't need to do the push manually:

let validationResults = new Array();



validationResults = InputDataMap.map(item => validateEntry(item));

You don't need async here because you do not need an await here. Now validationResults contains a list of Promises. You now need to use Promise.all to wait until those are resolved.

function ValidateAll(InputDataMap){

  let validationResults = InputDataMap.map(item => validateEntry(item));



  return Promise.all(validationResults);

}

Now ValidateAll will return a Promise that will resolve with an array containing the results of the validation.

You could shorten the code even more to:

function ValidateAll(InputDataMap){

  return Promise.all( InputDataMap.map(validateEntry) );

}

You have to return a Promise containing all the async operations, something like this:

function ValidateAll(InputDataMap) {

  return Promise.all(InputDataMap.map(item => validateEntry(item)));

}

I read that if you use the async/await keyword it will pause a function until the promise has been resolved, so I made changes, something like this:

Indeed it does pause the function but async(item) => {//Code} is another function unaffected by the outer function

async function ValidateAll(InputDataMap){

      let validationResults = ;

      for (item of InputDataMap) {

          let result = await validateEntry(item);

          validationResults.push(result);

      }

      return validationResults;      

});

Also notice the async keyword in front of the function declaration, which mean you have to use it via let results = await ValidateAll(inputData) or like ValidateAll(inputData).then(results => {//Code})

function ValidateAll(InputDataMap){

      return Promise.all(InputDataMap.map(item => validateEntry(item)))

});