README

A pure JavaScript implementation of Sass. Sass makes CSS fun again.

This package is a distribution of Dart Sass, compiled to pure JavaScript with no native code or external dependencies. It provides a command-line `sass` executable and a Node.js API.

- Usage
- API
- See Also
- Behavioral Differences from Ruby Sass

## Usage

You can install Sass globally using `npm install -g sass` which will provide access to the `sass` executable. You can also add it to your project using `npm install --save-dev sass`. This provides the executable as well as a library:

var sass = require('sass');
sass.render({file: scss_filename}, function(err, result) { /* ... */ });
// OR
var result = sass.renderSync({file: scss_filename});

See below for details on Dart Sass's JavaScript API.

## API

When installed via npm, Dart Sass supports a JavaScript API that's fully compatible with Node Sass (with a few exceptions listed below), with support for both the `render()` and `renderSync()` functions. See the Sass website for full API documentation!

Note however that by default, **`renderSync()` is more than twice as fast as `render()`** due to the overhead of asynchronous callbacks. To avoid this performance hit, `render()` can use the `fibers` package to call asynchronous importers from the synchronous code path. To enable this, pass the `Fiber` class to the `fiber` option:

var sass = require("sass");
var Fiber = require("fibers");
sass.render({
file: "input.scss",
importer: function(url, prev, done) {
// ...
},
fiber: Fiber
}, function(err, result) {
// ...
});

Both `render()` and `renderSync()` support the following options:

- `data`
- `file`
- `functions`
- `importer`
- `includePaths`
- `indentType`
- `indentWidth`
- `indentedSyntax`
- `linefeed`
- `omitSourceMapUrl`
- `outFile`
- `sourceMapContents`
- `sourceMapEmbed`
- `sourceMapRoot`
- `sourceMap`
- Only the `"expanded"` and `"compressed"` values of `outputStyle` are supported.

No support is intended for the following options:

- `precision`. Dart Sass defaults to a sufficiently high precision for all existing browsers, and making this customizable would make the code substantially less efficient.
- `sourceComments`. Source maps are the recommended way of locating the origin of generated selectors.

## See Also

- Dart Sass, from which this package is compiled, can be used either as a stand-alone executable or as a Dart library. Running Dart Sass on the Dart VM is substantially faster than running the pure JavaScript version, so this may be appropriate for performance-sensitive applications. The Dart API is also (currently) more user-friendly than the JavaScript API. See the Dart Sass README for details on how to use it.
- Node Sass, which is a wrapper around LibSass, the C++ implementation of Sass. Node Sass supports the same API as this package and is also faster (although it's usually a little slower than Dart Sass). However, it requires a native library which may be difficult to install, and it's generally slower to add features and fix bugs.

## Behavioral Differences from Ruby Sass

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.

1. `@extend` only accepts simple selectors, as does the second argument of `selector-extend()`. See issue 1599.
2. Subject selectors are not supported. See issue 1126.
3. Pseudo selector arguments are parsed as `<declaration-value>`s rather than having a more limited custom parsing. See issue 2120.
4. The numeric precision is set to 10. See issue 1122.
5. The indented syntax parser is more flexible: it doesn't require consistent indentation across the whole document. See issue 2176.
6. Colors do not support channel-by-channel arithmetic. See issue 2144.
7. Unitless numbers aren't `==` to unit numbers with the same value. In addition, map keys follow the same logic as `==`-equality. See issue 1496.
8. `rgba()` and `hsla()` alpha values with percentage units are interpreted as percentages. Other units are forbidden. See issue 1525.
9. Too many variable arguments passed to a function is an error. See issue 1408.
10. Allow `@extend` to reach outside a media query if there's an identical `@extend` defined outside that query. This isn't tracked explicitly, because it'll be irrelevant when issue 1050 is fixed.
11. Some selector pseudos containing placeholder selectors will be compiled where they wouldn't be in Ruby Sass. This better matches the semantics of the selectors in question, and is more efficient. See issue 2228.
12. The old-style `:property value` syntax is not supported in the indented syntax. See issue 2245.
13. The reference combinator is not supported. See issue 303.
14. Universal selector unification is symmetrical. See issue 2247.
15. `@extend` doesn't produce an error if it matches but fails to unify. See issue 2250.
16. Dart Sass currently only supports UTF-8 documents. We'd like to support more, but Dart currently doesn't support them. See dart-lang/sdk#11744, for example.

Disclaimer: this is not an official Google product.