Using Dart Sass

There are a few different ways to install and run Dart Sass, depending on your environment and your needs.

Standalone

You can download the standalone Dart Sass archive for your operating system—containing the Dart VM and the a snapshot of the Sass library—from the release page. Extract it, add the directory to your path, and the dart-sass executable is ready to run!

From npm

Dart Sass is available, compiled to JavaScript, as an npm package. You can install it globally using npm install -g dart-sass, or to your project using npm install dart-sass. This provides a dart-sass executable as well as a library:

var sass = require('dart-sass');

var result = sass.render({file: scss_filename});

The render() function will eventually support the same API as node-sass's, but today it only supports the file option.

From Pub

If you're a Dart user, you can install Dart Sass globally using pub global install dart-sass, which will provide a dart-sass executable. You can also add it to your pubspec and use it as a library:

import 'package:sass/sass.dart' as sass;

void main(List<String> args) {
  print(sass.render(args.first));
}

See the Dart API docs for details.

From Source

Assuming you've already checked out this repository:

Install Dart. If you download it manually, make sure the SDK's bin directory is on your PATH.
In this repository, run pub get. This will install Dart Sass's dependencies.
Run dart bin/sass.dart path/to/file.scss.

That's it!

Goals

Dart Sass is intended to eventually replace Ruby Sass as the canonical implementation of the Sass language. It has a number of advantages:

It's fast. The Dart VM is highly optimized, and getting faster all the time (for the latest performance numbers, see perf.md). It's much faster than Ruby, and not too far away from C.
It's portable. The Dart VM has no external dependencies and can compile applications into standalone snapshot files, so a fully-functional Dart Sass could be distributed as only three files (the VM, the snapshot, and a wrapper script). Dart can also be compiled to JavaScript, which would make it easy to distribute Sass through npm or other JS package managers.
It's friendlier to contributors. Dart is substantially easier to learn than Ruby, and many Sass users in Google in particular are already familiar with it. More contributors translates to faster, more consistent development.

Behavioral Differences

There are a few intentional behavioral differences between Dart Sass and Ruby Sass. These are generally places where Ruby Sass has an undesired behavior, and it's substantially easier to implement the correct behavior than it would be to implement compatible behavior. These should all have tracking bugs against Ruby Sass to update the reference behavior.

@extend only accepts simple selectors, as does the second argument of selector-extend(). See issue 1599.
Subject selectors are not supported. See issue 1126.
Pseudo selector arguments are parsed as <declaration-value>s rather than having a more limited custom parsing. See issue 2120.
The numeric precision is set to 10. See issue 1122.
The indented syntax parser is more flexible: it doesn't require consistent indentation across the whole document. See issue 2176.
Colors do not support channel-by-channel arithmetic. See issue 2144.
Unitless numbers aren't == to unit numbers with the same value. In addition, map keys follow the same logic as ==-equality. See issue 1496.

Disclaimer: this is not an official Google product.

License

kaelig/dart-sass

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