Embedded Sass Host

This package is an alternative to the sass package. It supports the same JS
API as sass and is maintained by the same team, but where the sass package
is pure JavaScript, sass-embedded is instead a JavaScript wrapper around a
native Dart executable. This means sass-embedded will generally be much faster
especially for large Sass compilations, but it can only be installed on the
platforms that Dart supports: Windows, Mac OS, and Linux.

Despite being different packages, both sass and sass-embedded are considered
"Dart Sass" since they have the same underlying implementation. Since the first
stable release of the sass-embedded package, both packages are released at the
same time and share the same version number.

Usage

This package provides the same JavaScript API as the sass package, and can be
used as a drop-in replacement:

 const sass = require('sass-embedded');

const result = sass.compile(scssFilename);

// OR

const result = await sass.compileAsync(scssFilename);

Unlike the sass package, the asynchronous API in sass-embedded will
generally be faster than the synchronous API since the Sass compilation logic is
happening in a different process.

See the Sass website for full API documentation.

Legacy API

The sass-embedded package also supports the older JavaScript API that's fully
compatible with Node Sass (with a few exceptions listed below), with support
for both the render() and renderSync() functions. This API is considered
deprecated and will be removed in Dart Sass 2.0.0, so it should be avoided in
new projects.

Sass's support for the legacy JavaScript API has the following limitations:

• Only the "expanded" and "compressed" values of outputStyle are
  supported.

• The sass-embedded package doesn't support the precision option. Dart
  Sass defaults to a sufficiently high precision for all existing browsers, and
  making this customizable would make the code substantially less efficient.

• The sass-embedded package doesn't support the [sourceComments] option.
  Source maps are the recommended way of locating the origin of generated
  selectors.

• The sass-embedded package doesn't support the indentWidth,
  indentType, or linefeed options. It implements the legacy API as a
  wrapper around the new API, and the new API has dropped support for these
  options.

How Does It Work?

The sass-embedded runs the Dart Sass embedded compiler as a separate
executable and uses the Embedded Sass Protocol to communicate with it over its
stdin and stdout streams. This protocol is designed to make it possible not only
to start a Sass compilation, but to control aspects of it that are exposed by an
API. This includes defining custom importers, functions, and loggers, all of
which are invoked by messages from the embedded compiler back to the host.

Although this sort of two-way communication with an embedded process is
inherently asynchronous in Node.js, this package supports the synchronous
compile() API using a custom synchronous message-passing library that's
implemented with the Atomics.wait() primitive. We hope to release this
library as a stand-alone package at some point in the future.

Disclaimer: this is not an official Google product.