SyncPromise.md

SyncPromise

The Promise brings great syntaxes: expressional error control with .then, .catch, .finally, and flat asynchronous programing with async/await. And we hope to use them for synchronous programing as well. That's why SyncPromise here.

Usage

The APIs of SyncPromise are almost all the same as Promise, only except the constructor.

import 'https://better-js.fenz.land/src/SyncPromise.js';

const foo= new SyncPromise( ()=> {
	if( ok )
		return someValue;
	else
		throw someReason;
}, );

// methods are all the same as Promise, but run synchronously
foo.then();
foo.catch();
foo.finally();

SyncPromise.resolve();
SyncPromise.reject();
SyncPromise.all();
SyncPromise.allSettled();
SyncPromise.race();
SyncPromise.any();
SyncPromise.try();

All of these methods return instances of SyncPromise (or Promise). So you can use promise chain too, that's run synchronously too.

foo
	.then(/*...*/)
	.then(/*...*/)
	.then(/*...*/)
	.then(/*...*/)
	.catch(/*...*/)
;

fallback to asynchronous Promise

If there is some asynchronous thing appear during the process, the SyncPromise will fallback to asynchronous Promise.

const promise= new SyncPromise( async ()=> {}, );

promise.constructor === Promise;

new SyncPromise( ()=> {}, ) // SyncPromise
	.then( ()=> {}, )       // SyncPromise
	.then( async ()=> {}, ) // Promise
	.then( ()=> {}, )       // Promise
;

In fact, you needn't to care about whether it is a SyncPromise or Promise in most cases. The SyncPromises can take every places of Promises.

You can await them as well, but because await is a asynchronous thing, SyncPromise will fallback to Promise after that.

console.log( '-1-', );

(async ()=> {
	console.log( '-2-', );
	
	await new SyncPromise( ()=> {}, );
	
	// We wish -4- logged before -3- too, but we cannot modify syntax feature itself
	console.log( '-4-', );
})();

console.log( '-3-', );