make-promises-safe 
A Happy Note
If you are using Node.js version 15+, the correct promise behaviour is already implemented and Node.js will safely behave on unhandled rejections similarly to its uncaught exception behaviour. If you are only using Node.js v15+ there is no need to use this module.
If you need to support older versions of Node.js - it is a good idea to use this module to ensure future compatibility with modern Node.js versions where the safe behaviour is the default one.
What this is
A node.js module to make the use of promises safe. It implements the deprecation DEP0018 of Node.js in versions 6+. Using Promises without this module might cause file descriptor and memory leaks.
It is important that this module is only used in top-level program code, not in reusable modules!
The Problem
Node.js crashes if there is an uncaught exception, while it does not
crash if there is an 'unhandledRejection', i.e. a Promise without a
.catch() handler.
If you are using promises, you should attach a .catch() handler
synchronously.
As an example, the following server will leak a file descriptor because
of a missing .catch() handler:
const http = require('http')
const server = http.createServer(handle)
server.listen(3000)
function handle (req, res) {
doStuff()
.then((body) => {
res.end(body)
})
}
function doStuff () {
if (Math.random() < 0.5) {
return Promise.reject(new Error('kaboom'))
}
return Promise.resolve('hello world')
}The Solution
make-promises-safe installs an process.on('unhandledRejection')
handler that prints the stacktrace and exits the process with an exit
code of 1, just like any uncaught exception.
Install
npm install make-promises-safe --save
Usage
'use strict'
require('make-promises-safe') // installs an 'unhandledRejection' handler
const http = require('http')
const server = http.createServer(handle)
server.listen(3000)
function handle (req, res) {
doStuff()
.then((body) => {
res.end(body)
})
}
function doStuff () {
if (Math.random() < 0.5) {
return Promise.reject(new Error('kaboom'))
}
return Promise.resolve('hello world')
}as a preloader
You can add this behavior to any Node.js application by using it as a preloader:
node -r make-promises-safe server.js
with core dumps
You can also create a core dump when an unhandled rejection occurs:
require('make-promises-safe').abort = true
With custom logging
You can add a custom logger to log errors in your own format. To do this override the logError property with a function that takes a single Error parameter. This defaults to console.error.
const makePromisesSafe = require('make-promises-safe');
makePromisesSafe.logError = function(err) {
// log the err object
}
License
MIT
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