Wait until all promises complete even if some rejected

Question

Let\'s say I have a set of Promises that are making network requests, of which one will fail:

// http://does-not-exist will throw a TypeError
va         


        

Answer 1

I know that this question has a lot of answers, and I'm sure must (if not all) are correct. However it was very hard for me to understand the logic/flow of these answers.

So I looked at the Original Implementation on Promise.all(), and I tried to imitate that logic - with the exception of not stopping the execution if one Promise failed.

  public promiseExecuteAll(promisesList: Promise[] = []): Promise<{ data: any, isSuccess: boolean }[]>
  {
    let promise: Promise<{ data: any, isSuccess: boolean }[]>;

    if (promisesList.length)
    {
      const result: { data: any, isSuccess: boolean }[] = [];
      let count: number = 0;

      promise = new Promise<{ data: any, isSuccess: boolean }[]>((resolve, reject) =>
      {
        promisesList.forEach((currentPromise: Promise, index: number) =>
        {
          currentPromise.then(
            (data) => // Success
            {
              result[index] = { data, isSuccess: true };
              if (promisesList.length <= ++count) { resolve(result); }
            },
            (data) => // Error
            {
              result[index] = { data, isSuccess: false };
              if (promisesList.length <= ++count) { resolve(result); }
            });
        });
      });
    }
    else
    {
      promise = Promise.resolve([]);
    }

    return promise;
  }

Explanation:
- Loop over the input promisesList and execute each Promise.
- No matter if the Promise resolved or rejected: save the Promise's result in a result array according to the index. Save also the resolve/reject status (isSuccess).
- Once all Promises completed, return one Promise with the result of all others.

Example of use:

const p1 = Promise.resolve("OK");
const p2 = Promise.reject(new Error(":-("));
const p3 = Promise.resolve(1000);

promiseExecuteAll([p1, p2, p3]).then((data) => {
  data.forEach(value => console.log(`${ value.isSuccess ? 'Resolve' : 'Reject' } >> ${ value.data }`));
});

/* Output: 
Resolve >> OK
Reject >> :-(
Resolve >> 1000
*/