Less 是一门 CSS 预处理语言，它扩充了 CSS 语言，增加了诸如变量、混合（mixin）、函数等功能，让 CSS 更易维护、方便制作主题、扩充。
Less 可以运行在 Node、浏览器和 Rhino 平台上。网上有很多第三方工具帮助你编译 Less 源码。
http://lesscss.org/less-preview/
Getting Started
Less is a CSS pre-processor, meaning that it extends the CSS language, adding features that allow variables, mixins, functions and many other techniques that allow you to make CSS that is more maintainable, themable and extendable.
Less runs inside Node, in the browser and inside Rhino. There are also many 3rd party tools that allow you to compile your files and watch for changes. The quickest place for first experiments with less is our online editor.
For example:
@base: #f938ab;
.box-shadow(@style, @c) when (iscolor(@c)) {
-webkit-box-shadow: @style @c;
box-shadow: @style @c;
}
.box-shadow(@style, @alpha: 50%) when (isnumber(@alpha)) {
.box-shadow(@style, rgba(0, 0, 0, @alpha));
}
.box {
color: saturate(@base, 5%);
border-color: lighten(@base, 30%);
div { .box-shadow(0 0 5px, 30%) }
}
compiles to
.box {
color: #fe33ac;
border-color: #fdcdea;
}
.box div {
-webkit-box-shadow: 0 0 5px rgba(0, 0, 0, 0.3);
box-shadow: 0 0 5px rgba(0, 0, 0, 0.3);
}
Using Less
Less can be used on the command line via npm, downloaded as a script file for the browser or used in a wide variety of third party tools. See the Usage section for more detailed information.
Installation
The easiest way to install Less on the server, is via npm, the node.js package manager, as so:
$ npm install -g less
Command-line Usage
Once installed, you can invoke the compiler from the command-line, as such:
$ lessc styles.less
This will output the compiled CSS to stdout. To save the CSS result to a file of your choice use:
$ lessc styles.less styles.css
To output minified you can CSS use clean-css plugin. When the plugin is installed, a minified CSS output is specified with --clean-css option:
$ lessc --clean-css styles.less styles.min.css
To see all the command line options run lessc without parameters or see Usage.
Usage in Code
You can invoke the compiler from node, as such:
var less = require(‘less‘);
less.render(‘.class { width: (1 + 1) }‘, function (e, output) {
console.log(output.css);
});
which will output
.class {
width: 2;
}
Configuration
You may pass some options to the compiler:
var less = require(‘less‘);
less.render(‘.class { width: (1 + 1) }‘,
{
paths: [‘.‘, ‘./lib‘], // Specify search paths for @import directives
filename: ‘style.less‘, // Specify a filename, for better error messages
compress: true // Minify CSS output
},
function (e, output) {
console.log(output.css);
});
See Usage for more information.
Third Party Tools
See the Usage section for details of other tools.
Command-line with Rhino
Each less.js release contains also rhino-compatible version.
Command line rhino version requires two files:
- less-rhino-<version>.js - compiler implementation,
- lessc-rhino-<version>.js - command line support.
Command to run the compiler:
java -jar js.jar -f less-rhino-<version>.js lessc-rhino-<version>.js styles.less styles.css
This will compile styles.less file and save the result to styles.css file. The output file parameter is optional. If it is missing, less will output the result to stdout.
Client-side Usage
Using less.js in the browser is great for development, but it‘s not recommended for production
Client-side is the easiest way to get started and good for developing with Less, but in production, when performance and reliability is important, we recommend pre-compiling using node.js or one of the many third party tools available.
To start off, link your .less stylesheets with the rel attribute set to "stylesheet/less":
<link rel="stylesheet/less" type="text/css" href="styles.less" />
Next, download less.js and include it in a <script></script> tag in the <head> element of your page:
<script src="less.js" type="text/javascript"></script>
Tips
- Make sure you include your stylesheets before the script.
- When you link more than one
.lessstylesheet each of them is compiled independently. So any variables, mixins or namespaces you define in a stylesheet are not accessible in any other. - Due to the same origin policy of browsers loading external resources requires enabling CORS
Browser Options
Options are defined by setting them on a global less object before the <script src="less.js"></script>:
<!-- set options before less.js script -->
<script>
less = {
env: "development",
async: false,
fileAsync: false,
poll: 1000,
functions: {},
dumpLineNumbers: "comments",
relativeUrls: false,
rootpath: ":/a.com/"
};
</script>
<script src="less.js"></script>
Or for brevity they can be set as attributes on the script and link tags (requires JSON.parse browser support or polyfill).
<script src="less.js" data-poll="1000" data-relative-urls="false"></script>
<link data-dump-line-numbers="all" data-global-vars=‘{ myvar: "#ddffee", mystr: "\"quoted\"" }‘ rel="stylesheet/less" type="text/css" href="less/styles.less">
Learn more about Browser Options
Get Less.js
Browser downloads
Download Source Code
Get the latest Less.js source code by downloading it directly from GitHub.
Clone or Fork via GitHub
Fork the project and send us a pull request!
Install with Bower
Install the Less.js project and JavaScript by running the following in the command line:
bower install less
Less CDN
<script src="//cdnjs.cloudflare.com/ajax/libs/less.js/2.5.3/less.min.js"></script>
License FAQs
Less.js is released under the Apache 2 License (though there are plans to dual license it). Copyright 2009-2015, Alexis Sellier and the Less Core Team (see about). Boiled down to smaller chunks, it can be described with the following conditions.
It allows you to:
- Freely download and use Less.js, in whole or in part, for personal, company internal or commercial purposes
- Use Less.js in packages or distributions that you create
It forbids you to:
- Redistribute any piece of Less.js without proper attribution
It requires you to:
- Include a copy of the license in any redistribution you may make that includes Less.js
- Provide clear attribution to The Less Core Team for any distributions that include Less.js
It does not require you to:
- Include the source of Less.js itself, or of any modifications you may have made to it, in any redistribution you may assemble that includes it
- Submit changes that you make to Less.js back to the Less.js project (though such feedback is encouraged)
The full Less.js license is located in the project repository for more information.
https://github.com/less/less.js
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