concise-object-stream

object-stream

A simplified API for working with node object streams

This module is inspired by Rod Vagg's through2 module but by focusing purely on object streams is able to provide a more concise API, including support for returning a value or promise from a transform function.

Getting started

Install via NPM

  npm i concise-object-stream --save

At it's simplest a transform stream can be created from function that returns the desired value to be queued or a promise for that value:

var objectStream = require('concise-object-stream')

getKeyStream()
    .pipe(objectStream.map(key => getObject(key)))
    .pipe(someOtherStream)

callback shorthand style is also supported:

getKeyStream()
    .pipe(objectStream.map((key, callback) => {
        const obj = getObject(key);
        callback(null, obj);
    }))
    .pipe(someOtherStream)

as is traditional style using this:

getKeyStream()
    .pipe(objectStream.map(function (key, callback) {
        const obj = getObject(key);
        this.push(obj);
        callback();
    }))
    .pipe(someOtherStream)

API

objectStream.map([options], [transform], [flush])

options

Options to be passed to the stream.Transform constructor, see here for available options.

getKeyStream()
    .pipe(objectStream.map({highWaterMark: 6}, key => getObject(key)))
    .pipe(someOtherStream)

transform

The transform function will be invoked with arguments object and callback. object is the callback object on the stream, callback indicates the end of the transform function and signal any errors.

getKeyStream()
    .pipe(objectStream.map(function (key, callback) {
        const obj = getObject(key);
        this.push(obj);
        callback();
    }))
    .pipe(someOtherStream)

callback can also be called with an object as a shorthand for queuing a single object on the stream:

getKeyStream()
    .pipe(objectStream.map((key, callback) => {
        const obj = getObject(key);
        callback(null, obj);
    }))
    .pipe(someOtherStream)

Instead of using callback a value may be returned from the transform function, if the return value is a promise then this will be resolved and the result queued.

getKeyStream()
    .pipe(objectStream.map(key => getObject(key)))
    .pipe(someOtherStream)

If a transform function is not supplied it will default to a pass-through stream.

flush

The flush function will be invoked with a single argument done which can be used to indicate the end of the flush function and signal any errors.

getKeyStream()
    .pipe(objectStream.map(function (key, callback) {
        const obj = getObject(key);
        this.push(obj);
        callback();
    }, function (done) {
        const finalObj = getFinalObj();
        this.push(obj);
        done();
    }))
    .pipe(someOtherStream)

Like the callback function, done supports a shorthand for queueing a single value:

getKeyStream()
    .pipe(objectStream.map((key, callback) => {
        const obj = getObject(key);
        callback(null, obj);
    }, done => {
        const finalObj = getFinalObj();
        done(null, obj);
    }))
    .pipe(someOtherStream)

flush also supports returning a value or promise, promises will be resolved and the result queued:

getKeyStream()
    .pipe(objectStream.map(key => getObject(key), () => getFinalObj()))
    .pipe(someOtherStream)

License

MIT