javascript - not able to execute the promise from array one by one

user_10686620 0
Viewed 123

I found that I cannot resolve the promises one by one.

This is my code

const promises = mkt.map((marketItem) => {
  return context.program.account.chain
    .fetch(marketItem[0].instrument)
    .then((instrumentRes) => {
      return Test(context, marketItem[0]).then(
        testResult => {
          return Promise.all([
            functionA(),
            functionB(),
          ]).then((result) => {
            return result
          });
        }
      );
    });
});
console.log(promises)
for (let i=0; i < promises.length; i++) {
  const val = await promises[i]();
  console.log(val);
}

error

promises[i]() is not a function

Why is that?How can I solve it?

promise reactjs javascript
2 Answers

promises[i]() is not a function

Correct, this is because promises is an array of Promise objects, not functions.

You can dump this promises array into Promise.all and wait for them all to resolve.

Promise.all(promises)
  .then(resolvedPromises => {
    // handle array of resolved promises
  });

but I am working on some real time update stuff. If I use Promise.all it will throw error Too many request, so I want to do it one by one to see the effect

For this then I think you want to iterate on the mkt array and wait for each created Promise to resolve. Refactor the mapping callback into a standalone function that you can manually invoke within the for-loop, awaiting the the Promise to settle.

const request = (marketItem) => {
  return context.program.account.chain
    .fetch(marketItem[0].instrument)
    .then((instrumentRes) => Test(context, marketItem[0]))
    .then(testResult => Promise.all([functionA(), functionB()]))
    .then((result) => result);
}

for (let i=0; i < mkt.length; i++) {
  try {
    const val = await request(mkt[i]);
    console.log(val);
  } catch(error) {
    // handle any error
  }
}
user_86908570

Just removing the () from the await call should already work.

  const val = await promises[i];

However keep in mind that all the promises have already been "started" (I don't know a better word for that) at that point and you're just retrieving the results or an error with the await call.

user_56182660
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