These Promise-related utilities boast 100% test coverage, ensuring robust reliability. The package, free of external dependencies, offers essential functions such as:

• repeat: Executes an operation repeatedly, very useful to collect all results through pagination.
• withRetry: Retries an operation until a specified condition is met.
• withConcurrency: Executes multiple operations with specified level of concurrency, and abort remaining operations when an error happens.
• inParallel: Executes multiple operations with specified level of concurrency, all operations are guaranteed to be executed regardless of any possible error.
• delayedResolve: Creates a Promise that resolves after a specified delay.
• delayedReject: Creates a Promise that rejects after a specified delay.
• timeoutResolve: Applies a timeout to a Promise and resolves with a specified result if the timeout occurs.
• timeoutReject: Applies a timeout to a Promise and rejects with a specified error/reason if the timeout occurs.
• promiseState: Retrieves the state of a Promise.
• synchronized: Provides mutual exclusion for concurrent operations using a lock mechanism, similar to synchronized in Java.

First add it as a dependency:

npm install @handy-common-utils/promise-utils

Then you can use it in the code:

import { PromiseUtils } from '@handy-common-utils/promise-utils';

// delayedResolve(...), delayedReject(...), promiseState(...)
const p1 = PromiseUtils.delayedResolve(50, 1);
const p2 = PromiseUtils.delayedReject(50, 2);
await expect(PromiseUtils.promiseState(p1)).eventually.eq(PromiseState.Pending);
await expect(PromiseUtils.promiseState(p2)).eventually.eq(PromiseState.Pending);
await PromiseUtils.delayedResolve(80);
await expect(PromiseUtils.promiseState(p1)).eventually.eq(PromiseState.Fulfilled);
await expect(PromiseUtils.promiseState(p2)).eventually.eq(PromiseState.Rejected);

// timeoutReject(...)
const p = PromiseUtils.timeoutReject(PromiseUtils.delayedReject(80, '1'), 10, '2');
await expect(p).to.be.rejectedWith('2');

// repeat(...)
async repeatFetchingItemsByPosition<T>(
  fetchItemsByPosition: (parameter: { position?: string }) => Promise<{ position?: string; items?: Array<T> }>,
) {
  return PromiseUtils.repeat(
    fetchItemsByPosition,
    response => response.position ? { position: response.position } : null,
    (collection, response) => response.items ? collection.concat(response.items) : collection,
    [] as Array<T>,
  );
}

You can either import and use the PromiseUtils class as shown above, or you can import its re-exported functions directly like below:

import { withRetry, inParallel, FIBONACCI_SEQUENCE, EXPONENTIAL_SEQUENCE } from '@handy-common-utils/promise-utils';

// withRetry(...)
const result = await withRetry(() => doSomething(), [100, 200, 300, 500, 800, 1000]);
const result2 = await withRetry(() => doSomething(), Array.from({length: 10}, (_v, i) => 1000 * Math.min(FIBONACCI_SEQUENCE[i], 10)), err => err.statusCode === 429);
const result3 = await withRetry(() => doSomething(), attempt => attempt <= 8 ? 1000 * Math.min(EXPONENTIAL_SEQUENCE[attempt - 1], 10) : undefined, err => err.statusCode === 429);
statusCode === 429);

// Capture errors in the returned array
const attributesAndPossibleErrors = await PromiseUtils.inParallel(5, topicArns, async (topicArn) => {
  const topicAttributes = (await sns.getTopicAttributes({ TopicArn: topicArn }).promise()).Attributes!;
  return topicAttributes;
});

// Abort on the first error
let results: Array<JobResult>;
try {
  results = await PromiseUtils.withConcurrency(100, jobs, async (job) => processor.process(job));
} catch (error) {
  // handle the error
}

• PromiseState

• PromiseUtils

• Const EXPONENTIAL_SEQUENCE: number[]

Array of 25 exponential numbers starting from 1 up to 33554432. It can be used to form your own backoff interval array.

Example

// 1ms, 2ms, 4ms, 8ms, 16ms, 32ms
PromiseUtils.withRetry(() => doSomething(), EXPONENTIAL_SEQUENCE.slice(0, 5), err => err.statusCode === 429);
// 1s, 2s, 4s, 8s, 10s, 10s, 10s, 10s, 10s, 10s
PromiseUtils.withRetry(() => doSomething(), Array.from({length: 10}, (_v, i) => 1000 * Math.min(EXPONENTIAL_SEQUENCE[i], 10)), err => err.statusCode === 429);
// with +-10% randomness: 1s, 2s, 4s, 8s
PromiseUtils.withRetry(() => doSomething(), FIBONACCI_SEQUENCE.slice(0, 4).map(n => 1000 * n * (1 + (Math.random() - 0.5) / 5)), err => err.statusCode === 429);

• Const FIBONACCI_SEQUENCE: number[]

Array of 25 Fibonacci numbers starting from 1 up to 317811. It can be used to form your own backoff interval array.

Example

// 1ms, 2ms, 3ms, 5ms, 8ms, 13ms
PromiseUtils.withRetry(() => doSomething(), FIBONACCI_SEQUENCE.slice(0, 5), err => err.statusCode === 429);
// 1s, 2s, 3s, 4s, 8s, 10s, 10s, 10s, 10s, 10s
PromiseUtils.withRetry(() => doSomething(), Array.from({length: 10}, (_v, i) => 1000 * Math.min(FIBONACCI_SEQUENCE[i], 10)), err => err.statusCode === 429);
// with +-10% randomness: 1s, 2s, 3s, 5s, 8s, 13s
PromiseUtils.withRetry(() => doSomething(), FIBONACCI_SEQUENCE.slice(0, 5).map(n => 1000 * n * (1 + (Math.random() - 0.5) / 5)), err => err.statusCode === 429);

▸ delayedReject<T, R>(ms, reason): Promise<T>

See delayedReject for full documentation.

Promise<T>

▸ delayedResolve<T>(ms, result?): Promise<T>

See delayedResolve for full documentation.

Promise<T>

▸ inParallel<Data, Result, TError>(parallelism, jobs, operation, options?): Promise<(Result | TError)[]>

See inParallel for full documentation.

Promise<(Result | TError)[]>

▸ promiseState(p): Promise<PromiseState>

See promiseState for full documentation.

Promise<PromiseState>

▸ repeat<Result, Param, Collection>(operation, nextParameter, collect, initialCollection, initialParameter?): Promise<Collection>

See repeat for full documentation.

Promise<Collection>

▸ synchronised<T>(lock, operation): Promise<T>

See synchronised for full documentation.

Promise<T>

▸ synchronized<T>(lock, operation): Promise<T>

See synchronized for full documentation.

Promise<T>

▸ timeoutReject<T, R>(operation, ms, rejectReason): Promise<T>

See timeoutReject for full documentation.

Promise<T>

▸ timeoutResolve<T>(operation, ms, result?): Promise<T>

See timeoutResolve for full documentation.

Promise<T>

▸ withConcurrency<Data, Result>(concurrency, jobs, operation): Promise<Result[]>

See withConcurrency for full documentation.

Promise<Result[]>

▸ withRetry<Result, TError>(operation, backoff, shouldRetry?): Promise<Result>

See withRetry for full documentation.

Promise<Result>

• new PromiseUtils()

▸ Static delayedReject<T, R>(ms, reason): Promise<T>

Creates a Promise that rejects after a specified number of milliseconds.

Promise<T>

A new Promise that rejects with the specified reason after the specified delay.

▸ Static delayedResolve<T>(ms, result?): Promise<T>

Creates a Promise that resolves after a specified number of milliseconds.

Promise<T>

A new Promise that resolves with the specified result after the specified delay.

▸ Static inParallel<Data, Result, TError>(parallelism, jobs, operation, options?): Promise<(Result | TError)[]>

Executes multiple jobs/operations in parallel. By default, all operations are executed regardless of any failures. In most cases, using withConcurrency might be more convenient.

By default, this function does not throw or reject an error when any job/operation fails. Errors from operations are returned alongside results in the returned array. This function only resolves when all jobs/operations are settled (either resolved or rejected).

If options.abortOnError is set to true, this function throws (or rejects with) an error immediately when any job/operation fails. In this mode, some jobs/operations may not be executed if one fails.

Promise<(Result | TError)[]>

A promise that resolves to an array containing the results of the operations. Each element is either a fulfilled result or a rejected error/reason. The results or errors in the returned array are in the same order as the corresponding elements in the jobs array.

Example

// Capture errors in the returned array
const attributesAndPossibleErrors: Array<JobResult|JobError> = await PromiseUtils.inParallel(5, topicArns, async (topicArn) => {
  const topicAttributes = (await sns.getTopicAttributes({ TopicArn: topicArn }).promise()).Attributes!;
  return topicAttributes;
});

// Abort on the first error
let results: Array<JobResult>;
try {
  results = await PromiseUtils.inParallel(100, jobs, async (job) => processor.process(job), { abortOnError: true });
} catch (error) {
  // handle the error
}

▸ Static promiseState(p): Promise<PromiseState>

Retrieves the state of the specified Promise. Note: The returned value is a Promise that resolves immediately.

Promise<PromiseState>

A Promise that resolves immediately with the state of the input Promise.

▸ Static repeat<Result, Param, Collection>(operation, nextParameter, collect, initialCollection, initialParameter?): Promise<Collection>

Executes an operation repeatedly and collects all the results. This function is very useful for many scenarios, such like client-side pagination.

Promise<Collection>

A promise that resolves to a collection of all the results returned by the operation function.

Example

const domainNameObjects = await PromiseUtils.repeat(
  pagingParam => apig.getDomainNames({limit: 500, ...pagingParam}).promise(),
  response => response.position? {position: response.position} : null,
  (collection, response) => collection.concat(response.items!),
  [] as APIGateway.DomainName[],
);

▸ Static synchronised<T>(lock, operation): Promise<T>

This is just another spelling of synchronized.

Promise<T>

The result of the operation function.

▸ Static synchronized<T>(lock, operation): Promise<T>

Provides mutual exclusion similar to synchronized in Java. Ensures no concurrent execution of any operation function associated with the same lock. The operation function has access to the state (when synchronized is called), settledState (when the operation function is called), and result (either the fulfilled result or the rejected reason) of the previous operation. If there is no previous invocation, state, settledState, and result will all be undefined.

Promise<T>

The result of the operation function.

▸ Static timeoutReject<T, R>(operation, ms, rejectReason): Promise<T>

Applies a timeout to a Promise or a function that returns a Promise. If the timeout occurs, the returned Promise rejects with the specified reason. If the timeout does not occur, the returned Promise resolves or rejects based on the outcome of the original Promise. If the rejectReason parameter is a function and the timeout does not occur, the function will not be called. Note: The rejection of the operation parameter is not handled by this function. You may want to handle it outside this function to avoid warnings like "(node:4330) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously."

Promise<T>

A new Promise that rejects with the specified reason if the timeout occurs.

▸ Static timeoutResolve<T>(operation, ms, result?): Promise<T>

Applies a timeout to a Promise or a function that returns a Promise. If the timeout occurs, the returned Promise resolves to the specified result. If the timeout does not occur, the returned Promise resolves or rejects based on the outcome of the original Promise. If the result parameter is a function and the timeout does not occur, the function will not be called. Note: The rejection of the operation parameter is not handled by this function. You may want to handle it outside this function to avoid warnings like "(node:4330) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously."

Promise<T>

A new Promise that resolves to the specified result if the timeout occurs.

▸ Static withConcurrency<Data, Result>(concurrency, jobs, operation): Promise<Result[]>

Executes multiple jobs/operations with a specified level of concurrency.

Unlike inParallel(...), this function may throw or reject an error when a job/operation fails. When an error is re-thrown, remaining operations will not be executed. If you want all the operations to always be executed, use inParallel instead.

Promise<Result[]>

A promise that resolves to an array containing the results from the operation function. The results in the returned array are in the same order as the corresponding elements in the jobs array.

Example

// At any time, there would be no more than 5 concurrency API calls. Error would be re-thrown immediately when it occurs.
const attributes = await PromiseUtils.withConcurrency(5, topicArns, async (topicArn) => {
  const topicAttributes = (await sns.getTopicAttributes({ TopicArn: topicArn }).promise()).Attributes!;
  return topicAttributes;
});

▸ Static withRetry<Result, TError>(operation, backoff, shouldRetry?): Promise<Result>

Repeatedly performs an operation until a specified criteria is met.

Promise<Result>

A promise of the operation result, potentially with retries applied.

Example

const result = await PromiseUtils.withRetry(() => doSomething(), [100, 200, 300, 500, 800, 1000]);
const result2 = await PromiseUtils.withRetry(() => doSomething(), Array.from({length: 10}, (_v, i) => 1000 * Math.min(FIBONACCI_SEQUENCE[i], 10), err => err.statusCode === 429);
const result3 = await PromiseUtils.withRetry(() => doSomething(), attempt => attempt <= 8 ? 1000 * Math.min(FIBONACCI_SEQUENCE[attempt - 1], 10) : undefined, err => err.statusCode === 429);

The state of a Promise can only be one of: Pending, Fulfilled, and Rejected.

• Fulfilled = "Fulfilled"

• Pending = "Pending"

• Rejected = "Rejected"