Less (stylesheet language)

Less
Designed by Alexis Sellier
Developer Alexis Sellier, Dmitry Fadeyev
First appeared 2009
Stable release 2.5.3[1] / September 25, 2015 (2015-09-25)
Typing discipline dynamic
Implementation language Javascript
OS Cross-platform
License Apache License 2
Filename extensions .less
Website lesscss.org
Influenced by
CSS, Sass
Influenced
Sass, Less Framework, Bootstrap

Less (sometimes stylized as LESS) is a dynamic style sheet language that can be compiled into Cascading Style Sheets (CSS) and run on the client side or server side.[2] Designed by Alexis Sellier, Less is influenced by Sass and has influenced the newer "SCSS" syntax of Sass, which adapted its CSS-like block formatting syntax.[3] Less is open source. Its first version was written in Ruby; however, in the later versions, use of Ruby has been deprecated and replaced by JavaScript. The indented syntax of Less is a nested metalanguage, as valid CSS is valid Less code with the same semantics. Less provides the following mechanisms: variables, nesting, mixins, operators and functions; the main difference between Less and other CSS precompilers being that Less allows real-time compilation via less.js by the browser.[4][2]

Variables

Less allows variables to be defined. Variables in Less are defined with an at sign (@). Variable assignment is done with a colon (:).

During translation, the values of the variables are inserted into the output CSS document.[2]

@pale-green-color: #4D926F;

#header {
  color: @pale-green-color;
}
h2 {
  color: @pale-green-color;
}

The code above in Less would compile to the following CSS code.

#header {
  color: #4D926F;
}
h2 {
  color: #4D926F;
}

Mixins

Mixins allow embedding all the properties of a class into another class by including the class name as one of its properties, thus behaving as a sort of constant or variable. They can also behave like functions, and take arguments. CSS does not support Mixins. Any repeated code must be repeated in each location. Mixins allow for more efficient and clean code repetitions, as well as easier alteration of code.[2]

.rounded-corners (@radius: 5px 10px 8px 2px) {
  -webkit-border-radius: @radius;
  -moz-border-radius: @radius;
  border-radius: @radius;
}

#header {
  .rounded-corners;
}
#footer {
  .rounded-corners(10px 25px 35px 0px);
}

The above code in Less would compile to the following CSS code:

#header {
  -webkit-border-radius: 5px 10px 8px 2px;
  -moz-border-radius: 5px 10px 8px 2px;
  border-radius: 5px 10px 8px 2px;
}
#footer {
  -webkit-border-radius: 10px 25px 35px 0px;
  -moz-border-radius: 10px 25px 35px 0px;
  border-radius: 10px 25px 35px 0px;
}

Less has a special type of ruleset called parametric mixins which can be mixed in like classes, but accepts parameters.

Nesting

CSS supports logical nesting, but the code blocks themselves are not nested. Less allows nesting of selectors inside other selectors. This makes inheritance clear and style sheets shorter.[2]

#header {
  h1 {
    font-size: 26px;
    font-weight: bold;
  }
  p {
    font-size: 16px;
    a {
      text-decoration: none;
      &:hover {
        border-width: 1px;
      }
    }
  }
}

The above code in Less would compile to the following CSS code:

#header h1 {
  font-size: 26px;
  font-weight: bold;
}
#header p {
  font-size: 16px;
}
#header p a {
  text-decoration: none;
}
#header p a:hover {
  border-width: 1px;
}

Functions and operations

Less allows operations and functions. Operations allow addition, subtraction, division and multiplication of property values and colors, which can be used to create complex relationships between properties. Functions map one-to-one with JavaScript code, allowing manipulation of values.

@the-border: 1px;
@base-color: #111;
@red:        #842210;

#header {
  color: @base-color * 3;
  border-left: @the-border;
  border-right: @the-border * 3;
}
#footer {
  color: @base-color + #003300;
  border-color: desaturate(@red, 10%);
}

The above code in Less would compile to the following CSS code:

#header {
  color: #333333;
  border-left: 1px;
  border-right: 3px;
}
#footer {
  color: #114411;
  border-color: #7d2717;
}

Comparison

Sass

Both Sass and Less are CSS preprocessors, which allow writing clean CSS in a programming construct instead of static rules.[5]

As of Less 1.4, Less supports nested, inherited rules via the &:extends and @extends pseudo-selector. Prior to this, a main difference between Less and other preprocessors like Sass was the lack of an @extends directive to support inheritance of rules across classes, leading to cleaner CSS with less duplication.

Less is inspired by Sass.[6] Sass was designed to both simplify and extend CSS, so things like curly braces were removed from the syntax. Less was designed to be as close to CSS as possible, so the syntax is identical to existing CSS code. As a result, existing CSS can be used as valid Less code.

The newer versions of Sass also introduced a CSS-like syntax called SCSS (Sassy CSS).[3]

For more syntax comparisons, see https://gist.github.com/674726.

Use on sites

Less can be applied to sites in a number of ways. One option is to include the less.js JavaScript file to convert the code on-the-fly. The browser then renders the output CSS. Another option is to render the Less code into pure CSS and upload the CSS to a site. With this option no .less files are uploaded and the site does not need the less.js JavaScript converter.

Less software

Name Description Software License Platform Functionality
WinLess GUI Less Compiler Apache 2.0[7] Windows Compiler
Crunch Less editor and compiler (requires Adobe AIR) GPL[8] Windows, Mac OS X Compiler
Editor
less.js-windows Simple command-line utility for Windows that will compile *.less files to CSS using less.js. MIT_License[9] Windows Compiler
less.app Less Compiler Proprietary Mac OS X Compiler
CodeKit Less Compiler Proprietary Mac OS X Compiler
LessEngine Less Compiler Free OpenCart Plugin Compiler
SimpLESS Less Compiler free but no explicit license[10] Windows
Mac OS X
Linux 		Compiler
Chirpy Less Compiler Ms-PL[11] Visual Studio Plugin Compiler
Mindscape Web Workbench Syntax highlighting and IntelliSense for Less and Sass Proprietary Visual Studio Plugin Compiler
Syntax Highlighting
Eclipse Plugin for Less Eclipse Plugin EPL 1.0[12] Eclipse Plugin Syntax highlighting
Content assist
Compiler
mod_less Apache2 module to compile Less on the fly Open Source Linux Compiler
grunt-contrib-less Node.js Grunt task to convert Less to CSS Open Source Node.js Compiler
Web Essentials Visual Studio extension with support for Less and Sass Apache 2.0 Windows Syntax highlighting, Content assist, Compiler
clessc Pure C++ compiler GPL at least Windows, Linux, MacOS Compiler

See also

References

  1. ↑ "CHANGELOG". GitHub.
  2. 1 2 3 4 5 Official Less website Official Less website
  3. 1 2 Sass and Less Sass and Less
  4. ↑ "css - Is there a SASS.js? Something like LESS.js?". Stack Overflow.
  5. ↑ What's Wrong With CSS What's Wrong With CSS
  6. ↑ About Less About
  7. ↑ WinLess github Issue "License Information"
  8. ↑ Crunch's LICENSE.txt at github Crunch's LICENSE.txt at github
  9. ↑ github license
  10. ↑ license file at github (placeholder)
  11. ↑ Chirpy License Information at CodePlex
  12. ↑ Eclipse Plugin for Less homepage Eclipse Plugin for Less homepage

External links

This article is issued from Wikipedia - version of the Monday, April 11, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.