lvyitian/deasync

Turns async function into sync via JavaScript wrapper of Node event loop

DeAsync

DeAsync turns async code into sync, implemented with a blocking mechanism by calling Node.js event loop at JavaScript layer. The core of deasync is written in C++.

This project is forked from abbr/deasync and rewritten in modern code, adding some new features: types, Promise support, and prebuild binaries.

Warning

Due to uv_run() is not reentrant, awaitSync and deasynced functions only work on top level, calling them from a callback will cause a deadlock.

Installation

npm install @kaciras/deasync

DeAsync downloads prebuild binary from GitHub releases during installation, if download fails, try to build locally. You can skip the install phase by setting the environment variable NO_PREBUILD=1.

DeAsync uses node-gyp to compile C++ source code, so to build Deasync you may need the compilers listed in node-gyp.

Usage

DeAsync exports only two APIs: deasync for callback-style functions, and awaitSync for Promises.

deasync(function)

Generic wrapper of async function with conventional API signature function(...args, (error, result) => {}). Returns result and throws error as exception if not null.

Sleep (a wrapper of setTimeout):

const { deasync } = require("@kaciras/deasync");

const sleep = deasync((timeout, callback) => {
	setTimeout(() => callback(null, "wake up!"), timeout);
});

console.log("Timestamp before: " + performance.now());
console.log(sleep(1000));
console.log("Timestamp after: " + performance.now());

awaitSync(promise)

Similar with the keyword await but synchronously.

const { awaitSync } = require("@kaciras/deasync");
const { performance } = require("perf_hooks");

const promise = new Promise(resolve => setTimeout(resolve, 1000)).then(() => "wake up!")

console.log("Timestamp before: " + performance.now());
console.log(awaitSync(promise));
console.log("Timestamp after: " + performance.now());

Recommendation

Unlike other (a)sync js packages that mostly have only syntactic impact, DeAsync also changes code execution sequence. As such, it is intended to solve niche cases like the above one. If all you are facing is syntactic problem such as callback hell, using a less drastic package implemented in pure js is recommended.