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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/
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);
}
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.
The easiest way to install Less on the server, is via npm, the node.js package manager, as so:
$ npm install -g less
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.
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;
}
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.
See the Usage section for details of other tools.
Each less.js release contains also rhino-compatible version.
Command line rhino version requires two files:
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.
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>
.less stylesheet each of them is compiled independently. So any variables, mixins or namespaces you define in a stylesheet are not accessible in any other.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
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.
The full Less.js license is located in the project repository for more information.
https://github.com/less/less.js
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原文地址：http://www.cnblogs.com/xgqfrms/p/4973122.html
