cop
v1.0.0
Published
Filter object streams
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cop - modify object stream
The cop Node.js package offers a Transform
stream to conventiently cop data from object streams.
Creating a Cop Object
Use require('cop')
to get a function
that returns a Transform
stream, configured in object mode, to which you can write arbitrary data. This constructor function takes either a String
or a function
as its sole argument.
Emitting Named Properties
Specify a String
to select a property, and the cop stream will emit the values of matching properties for all objects written to it. If an object doesn't have a property with this name, or the property's value is null
, the stream doesn't end, but just skips the object and moves on the next.
cop (key)
key
The name of the property of which to emit the value.
var cop = require('cop')
var stream = require('stream')
var objs = [
{ name: 'Moe' },
{ name: 'Larry' },
{ name: 'Curly' }
]
var stooges = new stream.Readable({ objectMode: true })
stooges._read = function () {
stooges.push(objs.shift() || null)
}
stooges
.pipe(cop('name'))
.pipe(process.stdout)
Transforming Objects
To apply custom transformations to each object, you can supply your own synchronous map function
, which is applied with each object and is expected to return an arbitrary object to be emitted by the cop stream. If you want to skip the current object, you can return null
or undefined
—the stream won't stop. For asynchronous work, of course, you should write your own stream.
cop (map)
map
Afunction
which is applied to each object written to the stream.
The following use case, streaming file entries with fstream and emitting just the filenames, filtering out directories; is the origin of this module. The filtering happens internally btw, sorry about that. But you get the point, you can do anything you want in the map function
.
var cop = require('cop')
var fstream = require('fstream')
function map (obj) {
return obj ? obj['path'] + '\n' : undefined
}
fstream.Reader({ path: __dirname })
.pipe(cop(map))
.pipe(process.stdout)
Installing Cop
With npm do:
$ npm install cop