sass

What is sass?

The sass npm package is a preprocessor scripting language that is interpreted or compiled into Cascading Style Sheets (CSS). It enables developers to use variables, nested rules, mixins, functions, and more, which can help in writing CSS in a more structured and maintainable way.

What are sass's main functionalities?

Variables

Variables allow you to store values that you can reuse throughout your stylesheet.

$primary-color: #333;

body {
  color: $primary-color;
}

Nesting

Nesting enables you to nest your CSS selectors in a way that follows the same visual hierarchy of your HTML.

nav {
  ul {
    margin: 0;
    padding: 0;
    list-style: none;
  }

  li { display: inline-block; }

  a {
    display: block;
    padding: 6px 12px;
    text-decoration: none;
  }
}

Partials and Import

Partials are Sass files named with a leading underscore. You can import these partials into other Sass files to modularize your CSS and help keep things easier to maintain.

// _reset.scss
html,
body,
ul,
ol {
  margin: 0;
  padding: 0;
}

// main.scss
@import 'reset';
body {
  font-family: sans-serif;
}

Mixins

Mixins allow you to define styles that can be reused throughout your stylesheet.

@mixin border-radius($radius) {
  -webkit-border-radius: $radius;
     -moz-border-radius: $radius;
      -ms-border-radius: $radius;
          border-radius: $radius;
}

.box { @include border-radius(10px); }

Extend/Inheritance

Extend/Inheritance lets you share a set of CSS properties from one selector to another.

.message {
  border: 1px solid #ccc;
  padding: 10px;
  color: #333;
}

.success {
  @extend .message;
  border-color: green;
}

Operators

Sass supports standard math operators like +, -, *, /, and %.

.container {
  width: 100%;
}
.article {
  width: 600px / 960px * 100%;
}

Other packages similar to sass

less

Less is a backward-compatible language extension for CSS. It provides similar features to Sass, such as variables, mixins, and nesting. However, Less uses JavaScript for compilation, whereas Sass was originally written in Ruby and now primarily uses a C implementation (Dart Sass).

stylus

Stylus is a preprocessor that offers a more flexible syntax than Sass and Less, with optional semicolons and braces. It also provides powerful features like variable interpolation and iteration. Stylus can be more terse and expressive in some cases but might have a steeper learning curve for those used to more traditional CSS syntax.

postcss

PostCSS is a tool for transforming CSS with JavaScript plugins. While it is not a preprocessor in the traditional sense, it can be used to achieve many of the same goals as Sass through its extensive plugin ecosystem. PostCSS is highly customizable and can be tailored to specific build processes and requirements.

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
• 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:

const sass = require('sass');

const result = sass.compile(scssFilename);

// OR

// Note that `compileAsync()` is substantially slower than `compile()`.
const result = await sass.compileAsync(scssFilename);

See the Sass website for full API documentation.

Legacy API

Dart Sass also supports an 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.

• Dart Sass 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.

• Dart Sass doesn't support the sourceComments option. 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.

Changelog

1.58.0

• Remove sourcemap comments from Sass sources. The generated sourcemap comment for the compiled CSS output remains unaffected.

• Fix a bug in @extend logic where certain selectors with three or more combinators were incorrectly considered superselectors of similar selectors with fewer combinators, causing them to be incorrectly trimmed from the output.

• Produce a better error message for a number with a leading + or -, a decimal point, but no digits.

• Produce a better error message for a nested property whose name starts with --.

• Fix a crash when a selector ends in an escaped backslash.

• Add the relative length units from CSS Values 4 and CSS Contain 3 as known units to validate bad computation in calc.

Command Line Interface

• The --watch flag will now track loads through calls to meta.load-css() as long as their URLs are literal strings without any interpolation.