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Original documentation

This middleware was created to allow processing of Less files for Connect JS framework and by extension the Express JS framework.

Installation

npm install less-middleware --save

Usage

lessMiddleware(source, [{options}])

Express

var lessMiddleware = require('less-middleware');

var app = express();
app.use(lessMiddleware(__dirname + '/public'));
app.use(express.static(__dirname + '/public'));

options

The following options can be used to control the behavior of the middleware:

Option	Description	Default
debug	Show more verbose logging?	false
dest	Destination directory to output the compiled .css files.	Same directory as less source files.
force	Always re-compile less files on each request.	false
once	Only recompile once after each server restart. Useful for reducing disk i/o on production.	false
pathRoot	Common root of the source and destination. It is prepended to both the source and destination before being used.	null
postprocess	Object containing functions relevant to postprocessing data.
postprocess.css	Function that modifies the compiled css output before being stored.	function(css, req){...}
preprocess	Object containing functions relevant to preprocessing data.
preprocess.less	Function that modifies the raw less output before being parsed and compiled.	function(src, req){...}
preprocess.path	Function that modifies the less pathname before being loaded from the filesystem.	function(pathname, req){...}
preprocess.importPaths	Function that modifies the import paths used by the less parser per request.	function(paths, req){...}
render	Options for the less render. See the "render Options" section below.	…
storeCss	Function that is in charge of storing the css in the filesystem.	function(pathname, css, req, next){...}
cacheFile	Path to a JSON file that will be used to cache less data across server restarts. This can greatly speed up initial load time after a server restart - if the less files haven't changed and the css files still exist, specifying this option will mean that the less files don't need to be recompiled after a server restart.

render Options

The options.render is passed directly into the less.render with minimal defaults or changes by the middleware.

The following are the defaults used by the middleware:

Option	Default
compress	auto
yuicompress	false
paths	[]

Examples

Common examples of using the Less middleware are available in the wiki.

Troubleshooting

My less never recompiles, even when I use {force: true}!

Make sure you're declaring less-middleware before your static middleware, if you're using the same directory, e.g. (with express):

var lessMiddleware = require('less-middleware');

var app = express();
app.use(lessMiddleware(__dirname + '/public'));
app.use(express.static(__dirname + '/public'));

not

var lessMiddleware = require('less-middleware');

var app = express();
app.use(express.static(__dirname + '/public'));
app.use(lessMiddleware(__dirname + '/public'));

IIS

If you are hosting your app on IIS you will have to modify your web.config file in order to allow NodeJS to serve your CSS static files. IIS will cache your CSS files, bypassing NodeJS static file serving, which in turn does not allow the middleware to recompile your LESS files.