p-some-first

p-some-first

Like Promise.all/Promise.any but only returns the first resolved value.

import PCancelable from "p-cancelable";
import pSomeFirst from "p-some-first";

(async () => {
	await pSomeFirst([
		new PCancelable((resolve) => setTimeout(() => resolve(1), 1000)),
		new PCancelable((resolve) => resolve(2)),
	]);
	// resolves to 1

	await pSomeFirst([
		new PCancelable((resolve, reject) => reject("error message")),
		new PCancelable((resolve, reject) => reject(new Error("intentional"))),
		new PCancelable((resolve, reject) => reject(42)),
	]);
	// rejects with ["error message", new Error("intentional"), 42]

	await pSomeFirst(
		[
			new PCancelable((resolve, reject) => reject("error message")),
			new PCancelable((resolve, reject) =>
				reject(new Error("intentional"))
			),
			new PCancelable((resolve, reject) => reject(42)),
		],
		7
	);
	// resolves to the fallback value (7)
})();

See the tests for more examples.

Cancelable Promises SHOULD be used otherwise there is hardly any difference between using p-some-first and this:

Promise.allSettled([
	Promise.reject(new Error("something")),
	Promise.resolve(42),
]).then((rr) => {
	return rr.find((r) => r.status === "fulfilled").value;
});

By using cancelable Promises, after one Promise resolves, all remaining Promises can be canceled and pSomeFirst will return without waiting for all promises to settle. Cancelable Promises will also help to minimize any errant UnhandledPromiseRejectionWarnings. Until JavaScript gets a way to cancel native Promises, you can use a library like p-cancelable or Bluebird to create cancelable Promises.

If cancelable Promises are not used (in a Node.js environment), a process warning will be emitted notifying you about this.

Changelog

1.1.0 (2020-05-17)

Features

• be more lax about accepted Promise types (9c61735)