Promise Ex

Provides additional functions for working with promises.

Function: createPromise

The createPromise function will create a promise and return it along with the resolve and reject functions.

Signature

createPromise<VALUE = unknown> () => iPromiseSet<VALUE>

Return

Returns the promise, and resolve and reject functions.

Usage

const { promise, resolve, reject } = createPromise<string>();
promise.then(console.info);
resolve('Supercalifragilisticexpialidocious!');

Function: isPromiseLike

The isPromiseLike checks if a value looks like a promise (i.e. has then and catch functions).

Signature

isPromiseLike<VALUE> (value: unknown) => value is Promise<VALUE>

Return

Returns true if the value looks like a promise.

Usage

isPromiseLike('Supercalifragilisticexpialidocious!') // Return false
isPromiseLike(Promise.resolve('Supercalifragilisticexpialidocious!')) // Return true

Function: promiseSingle

Defines a callback that will only allow single instance to run at a time. If a promise is already running, it will return the same promise.

Signature

promiseSingle<ACTION> (action: Function) => Promise<unknown> | unknown

Return

Returns a function. Calling this function will return a promise. Subsequent calls will be ignored until the current promise has been resolved.

Usage

const action = promiseSingle(async (src: string) =>
{
	const res = await fetch(src);
	return await res.json();
});

action('https://www.example.com');
action('https://www.example.com'); // Ignored because first call to action is still pending. Await the first call to make subsequent calls.

Function: promiseChain

Defines a callback that will call subsequent calls sequentially. If a promise is already running, it will return the same promise.

Signature

promiseChain<ACTION> (action: Function) => Promise<unknown> | unknown

Return

Returns a function. Calling this function will return a promise. Subsequent calls will be queued and called sequentially after the previous call has been resolved.

Usage

const action = promiseChain(async (src: string) =>
{
	const res = await fetch(src);
	return await res.json();
});

action('https://www.example.com');
action('https://www.example.com'); // Ignored because first call to action is still pending. Await the first call to make subsequent calls.

Type: tOptionalPromise

Defines an scenario where a value could be a promise or raw value.

tOptionalPromise<VALUE = unknown> = Promise<VALUE> | VALUE

Types: iPromiseSet, tPromiseResolveFn, tPromiseRejectFn

type tPromiseResolveFn<VALUE = unknown> = Parameters<ConstructorParameters<typeof Promise<VALUE>>[0]>[0];
type tPromiseRejectFn<VALUE = unknown> = Parameters<ConstructorParameters<typeof Promise<VALUE>>[0]>[1];

interface iPromiseSet<VALUE>
{
	promise: Promise<VALUE>;
	resolve: tPromiseResolveFn<VALUE>;
	reject: tPromiseRejectFn<VALUE>;
}