| Appeared in | 2009 |
|---|---|
| Designed by | Alexis Sellier |
| Developer | Alexis Sellier, Dmitry Fadeyev |
| Stable release | 1.1.4 (July 19, 2011) |
| Typing discipline | dynamic |
| Influenced by | CSS, Sass |
| Influenced | Sass, Less Framework |
| OS | Cross-platform |
| License | Apache 2 License |
| Usual filename extensions | .less |
| Website | lesscss.org |
LESS is a dynamic stylesheet language designed by Alexis Sellier. It is influenced by Sass and has influenced newer "SCSS" syntax of Sass, which adapted its CSS like block formatting syntax.[1]
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.[2]
LESS can run on the client-side (Internet Explorer 6+, WebKit, Firefox) and server-side, with Node.js or Rhino (JavaScript engine).[2]
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Less allows variables to be defined. Less variables 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]
@color: #4D926F;
#header {
color: @color;
}
h2 {
color: @color;
}
The above code in LESS would compile to following CSS code.
#header {
color: #4D926F;
}
h2 {
color: #4D926F;
}
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_(programming)|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) {
border-radius: @radius;
-webkit-border-radius: @radius;
-moz-border-radius: @radius;
}
#header {
.rounded-corners;
}
#footer {
.rounded-corners(10px);
}
The above code in LESS would compile to following CSS code:
#header {
border-radius: 5px;
-webkit-border-radius: 5px;
-moz-border-radius: 5px;
}
#footer {
border-radius: 10px;
-webkit-border-radius: 10px;
-moz-border-radius: 10px;
}
LESS has a special type of ruleset called parametric mixins which can be mixed in like classes, but accepts parameters.
CSS does support logical nesting, but the code blocks themselves are not nested. Less allows to nest selectors inside other selectors. This makes inheritance clear and style sheets shorter.[2]
#header {
h1 {
font-size: 26px;
font-weight: bold;
}
p { font-size: 12px;
a { text-decoration: none;
&:hover { border-width: 1px }
}
}
}
The above code in LESS would compile to following CSS code:
#header h1 {
font-size: 26px;
font-weight: bold;
}
#header p {
font-size: 12px;
}
#header p a {
text-decoration: none;
}
#header p a:hover {
border-width: 1px;
}
Less allows operations and functions. Operations allows to add, subtract, divide and multiply property values and colors, which can be used to create complex relationships between properties. Functions map one-to-one with JavaScript code, allowing to manipulate values.
@the-border: 1px;
@base-color: #111;
@red: #842210;
#header {
color: @base-color * 3;
border-left: @the-border;
border-right: @the-border * 2;
}
#footer {
color: @base-color + #003300;
border-color: desaturate(@red, 10%);
}
The above code in LESS would compile to following CSS code:
#header {
color: #333;
border-left: 1px;
border-right: 2px;
}
#footer {
color: #114411;
border-color: #7d2717;
}
Both Sass and LESS are CSS preprocessors, which allow writing clean CSS in a programming construct instead of static rules.[3]
LESS is inspired by Sass.[4] 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).[1]
For more of syntax comparition see https://gist.github.com/674726
ZUSS is inspired by LESS. The syntax is similar, except it is tailored for Java programming language. Unlike LESS, it doesn't require the JavaScript interpreter (Rhino), and it allows ZUSS to invoke Java methods directly.
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 it to render the less code into pure css prior to uploading the results to a site. Once the code is converted into pure css, it is then uploaded onto a site, however no .less files are uploaded and nor does the site need the less.js javascript converter.
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