Question

2795. Parallel Execution of Promises for Individual Results Retrieval

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Description

Given an array functions, return a promise promise. functions is an array of functions that return promises fnPromise. Each fnPromise can be resolved or rejected.  

If fnPromise is resolved:

    obj = { status: "fulfilled", value: _resolved value_}

If fnPromise is rejected:

    obj = { status: "rejected", reason: _reason of rejection (catched error message)_}

The promise should resolve with an array of these objects obj. Each obj in the array should correspond to the promises in the original array function, maintaining the same order.

Try to implement it without using the built-in method Promise.allSettled().

 

Example 1:

Input: functions = [
  () => new Promise(resolve => setTimeout(() => resolve(15), 100))
]
Output: {"t":100,"values":[{"status":"fulfilled","value":15}]}
Explanation: 
const time = performance.now()
const promise = promiseAllSettled(functions);
               
promise.then(res => {
  const out = {t: Math.floor(performance.now() - time), values: res}
  console.log(out) // {"t":100,"values":[{"status":"fulfilled","value":15}]}
})

The returned promise resolves within 100 milliseconds. Since promise from the array functions is fulfilled, the resolved value of the returned promise is set to [{"status":"fulfilled","value":15}].

Example 2:

Input: functions = [
  () => new Promise(resolve => setTimeout(() => resolve(20), 100)), 
  () => new Promise(resolve => setTimeout(() => resolve(15), 100))
]
Output: 
{
  "t":100,
  "values": [
      {"status":"fulfilled","value":20},
      {"status":"fulfilled","value":15}
  ]
}
Explanation: The returned promise resolves within 100 milliseconds, because the resolution time is determined by the promise that takes the longest time to fulfill. Since promises from the array functions are fulfilled, the resolved value of the returned promise is set to [{"status":"fulfilled","value":20},{"status":"fulfilled","value":15}].

Example 3:

Input: functions = [
    () => new Promise(resolve => setTimeout(() => resolve(30), 200)), 
    () => new Promise((resolve, reject) => setTimeout(() => reject("Error"), 100))
]
Output:
{
  "t":200,
  "values": [
    {"status":"fulfilled","value":30},
    {"status":"rejected","reason":"Error"}
  ]
}
Explanation: The returned promise resolves within 200 milliseconds, as its resolution time is determined by the promise that takes the longest time to fulfill. Since one promise from the array function is fulfilled and another is rejected, the resolved value of the returned promise is set to an array containing objects in the following order: [{"status":"fulfilled","value":30}, {"status":"rejected","reason":"Error"}]. Each object in the array corresponds to the promises in the original array function, maintaining the same order.

 

Constraints:

• 1 <= functions.length <= 10

Solutions

Solution 1

type FulfilledObj = {
  status: 'fulfilled';
  value: string;
};
type RejectedObj = {
  status: 'rejected';
  reason: string;
};
type Obj = FulfilledObj | RejectedObj;

function promiseAllSettled(functions: Function[]): Promise<Obj[]> {
  return new Promise(resolve => {
    const res: Obj[] = [];
    let count = 0;
    for (let i in functions) {
      functions[i]()
        .then(value => ({ status: 'fulfilled', value }))
        .catch(reason => ({ status: 'rejected', reason }))
        .then(obj => {
          res[i] = obj;
          if (++count === functions.length) {
            resolve(res);
          }
        });
    }
  });
}

/**
 * const functions = [
 *  () => new Promise(resolve => setTimeout(() => resolve(15), 100))
 * ]
 * const time = performance.now()
 *
 * const promise = promiseAllSettled(functions);
 *
 * promise.then(res => {
 *   const out = {t: Math.floor(performance.now() - time), values: res}
 *   console.log(out) // {"t":100,"values":[{"status":"fulfilled","value":15}]}
 * })
 */

/**
 * @param {Array<Function>} functions
 * @return {Promise}
 */
var promiseAllSettled = function (functions) {
  return new Promise(resolve => {
    const res = [];
    let count = 0;
    for (let i in functions) {
      functions[i]()
        .then(value => ({ status: 'fulfilled', value }))
        .catch(reason => ({ status: 'rejected', reason }))
        .then(obj => {
          res[i] = obj;
          if (++count === functions.length) {
            resolve(res);
          }
        });
    }
  });
};