Highland

The high-level streams library for Node.js and the browser.
View the Highland website for more in-depth
documentation.

Introduction

Re-thinking the JavaScript
utility belt,
Highland manages synchronous and asynchronous code easily, using nothing more than
standard JavaScript and Node-like Streams.
You may be familiar with Promises, EventEmitters and callbacks, but moving
between them is far from seamless. Thankfully, there exists a deeper abstraction
which can free our code. By updating the tools we use on Arrays, and applying them
to values distributed in time instead of space, we can discard plumbing and
focus on the important things. With Highland, you can switch between
synchronous and asynchronous data sources at will, without having to
re-write your code. Time to dive in!

Made by @caolan, with help and patience from friends 😃

Highland v3

This branch tracks the ongoing development of version 3.0, which will feature a
rewritten Highland core implementation, extensibility support, limited stream
lifecycle, and some breaking changes to certain transforms. See
#179 and the 3.x
label
for more details. New features will only be added to this branch. However,
until 3.0 is released, we will still be doing bug fixes for the 2.x releases.
See the 2.x branch for those
files.

Currently, the code is in a semi-stable state. The only major missing feature
is onDestroy for higher-level
transforms. To try out the new
goodness, install the next tag from NPM.

npm install --save highland@next

Interoperability

Highland implements the Fantasy
Land
Alternative,
Filterable, and
Monad
specifications.

Highland supports
Transducers via the
transduce transform.

Examples

Usage as a Node.js module

var _ = require('highland');

Converting to/from Highland Streams

_([1,2,3,4]).toArray(function (xs) {
    // xs is [1,2,3,4]
});

Mapping over a Stream

var doubled = _([1,2,3,4]).map(function (x) {
    return x * 2;
});

Reading files in parallel (4 at once)

var data = _(filenames).map(readFile).parallel(4);

Handling errors

data.errors(function (err, rethrow) {
    // handle or rethrow error
});

Piping to a Node Stream

data.pipe(output);

Piping in data from Node Streams

var output = fs.createWriteStream('output');
var docs = db.createReadStream();

// wrap a node stream and pipe to file
_(docs).filter(isBlogpost).pipe(output);

// or, pipe in a node stream directly:
var through = _.pipeline(_.filter(isBlogpost));
docs.pipe(through).pipe(output);

Handling events

var clicks = _('click', btn).map(1);
var counter = clicks.scan(0, _.add);

counter.each(function (n) {
    $('#count').text(n);
});

Learn more at https://caolan.github.io/highland/