The pn library gives you the Promise-using node standard library you've always dreamed of. Think "Promised Node" when saying it.

Just about every node standard library method that takes a callback will now return a Promise iff no callback is supplied. But existing code that passes callbacks will still work fine --- and fast: No unnecessary Promises are created if you supply a callback.

The wrappers are generated automatically by a script, with a table to handle exceptions and odd cases. See below for more details.

npm install pn

var fs = require('pn/fs');
fs.writeFile('foo', 'bar', 'utf-8').then(function() { console.log('done'); });
// But you can use callbacks, too -- existing code won't break.
fs.writeFile('foo', 'bat', 'utf-8', function(err) { console.log('yay'); });

This library uses node native promises (ie global.Promise) by default, and thus works with node >= 0.11.

You can use core-js or es6-shim to add ES6 Promises to earlier versions of node, for example:

require('es6-shim');
var fs = require('pn/fs');

Just be sure that es6-shim is loaded before the pn package in that case.

You might also want to look into packages like prfun which add some helpers to make working with native promises much more fun.

In particular, the Promise#done method is very useful when debugging, at least until v8's native Promise debugging capabilities are completed.

You can also specify a custom Promise type to use, as follows:

var MyPromise = require('prfun');  // Use prfun's Promises, for example.
require('pn/_promise')(MyPromise); // This only needs to be done once.

The wrappers are automatically generated by scripts/generate.js; there is a table in that file which specifies all the odd cases.

In general: if the node API has a callback which takes multiple value arguments, the Promise returned will be an object with named fields corresponding to the different values. If the node API takes a callback and returns a value, pn will return the original value with a nonenumerable field named promise corresponding to the callback. Combining these two cases:

var child_process = require('pn/child_process');
var cp = child_process.execFile('true');
console.log('pid', cp.pid);
cp.promise.then(function(result) {
  console.log('stdout: ', result.stdout);
  console.log('stderr: ', result.stderr);
});

• child_process: The exec and execFile methods promise a object with fields named stdout and stderr. They return a ChildProcess object with a nonenumerable field named promise corresponding to the callback.
• crypto: The randomBytes and pseudoRandomBytes methods are now always asynchronous, returning a Promise if no callback is supplied. Use the new randomBytesSync and pseudoRandomBytesSync methods if you want synchronous computation. This is backwards incompatible with existing node code.
• dns: The lookupService method promises an object with fields named hostname and service.
• fs: The exists method doesn't pass an error to its callback. The promisied version will never reject. The write method promises an object with fields named written and data. The read method promises an object with fields named read and data.
• http, https: The request and get methods return a ClientRequest object with a nonenumerable field named promise, which will resolve to an IncomingMessage object.
• process: You can defer computation to the next tick with require('pn/process').nextTick().then(function(){...})
• tls: The connect and createServer return objects with a nonenumerable field named promise.

There are a few object methods which are not promisified by this package:

• domain: Domain#bind, Domain#intercept
• http,https: ClientRequest#setTimeout, IncomingMessage#setTimeout, Server#setTimeout, ServerResponse#setTimeout, Server#listen, Server#close
• net: Server#listen, Server#close, Server#getConnections, Socket#write, Socket#setTimeout
• readline: Interface#question
• stream: Writable#write, Writable#end
• dgram: Socket#send, Socket#bind.

Here are some other packages with similar aims:

• promised-node
• then-fs
• final-fs

Copyright (c) 2014-2018 C. Scott Ananian

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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