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express middleware for artifact free LESS compiling

Why another LESS middleware?

All existing LESS middlewares for express use a file based approach. This is great for big projects that require complex structures and high performance, yet this comes with two drawbacks: they generate build artifacts and complex setup. Sometimes you just want your app to serve a single CSS resource.


Install from npm:

$ npm install less-express --save


A simple example showing you how to serve the compiled version of ./public/stylesheets/app.less at /css/app.css:

var lessExpress = require('less-express');
app.get('/css/app.css', lessExpress('./public/stylesheets/app.less'));


You can configure the middleware by passing options to LESS or the middleware itself:

app.get('/css/app.css', lessExpress('./public/stylesheets/app.less', lessOptions, middlewareOptions));

lessOptions will be passed through to LESS. See the LESS documentation for available configuration. The following middlewareOptions are available for the middleware:

  • cache: TTL in milliseconds that compilation results will be cached. When true is passed the cache will keep the initial compilation result infinitely. By default the middleware uses infinite caching in production. If you want to disable this pass false.
  • precompile: Tell the middleware to precompile the stylesheet on application startup. This is happening per default in production and can be disabled by passing false. If you explicitly set cache to false this will do nothing.
  • stale: If true then the middleware will return a stale cache of the stylesheet, if available, when a compilation error is encountered. This is false by default. If you explicitly set cache to false this will do nothing.
  • passThru: If true then the middleware will not send the response and instead will assign the resulting stylesheet to res.locals.lessCss using the given location and call the next middleware. i.e
lessExpress.options({passThru: true});
app.get('/css/app.css', lessExpress('./public/stylesheets/app.less'), function (req, res, next) {
    var css = res.locals.lessCss['./public/stylesheets/app.less'];

This is useful for extra processing you may want to apply after compilation, but before sending the response. This is false by default.

You can also set global configuration options that will be applied to all calls by using #lessOptions and #options:

lessExpress.options({cache: false});
lessExpress.lessOptions({plugins: [cleanCSS]});

Options passed to the function invocation will take precedence:

lessExpress.options({cache: false});
app.get('/css/app.css', lessExpress('./public/stylesheets/app.less', {}, {cache: 3600})); // will cache


MIT © Frederik Ring



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