pn
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
Promise
s 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.
Installation
npm install pn
Usage
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.
Custom Promise types
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.
Exceptions and odd cases
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
.
Related packages
Here are some other packages with similar aims:
License
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.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.