Registry / http-networking / less-middleware

less-middleware

library3.1.0jsnpmunverified

less-middleware is an HTTP middleware specifically designed to process LESS CSS files for web servers built with Connect.js or Express.js. It compiles .less files into .css on-the-fly when requested, or upon server restart with caching, and serves the resulting CSS. The current stable version, 3.1.0, is compatible with Less.js 3.9. While not on a strict schedule, releases typically follow major Less.js updates to maintain compatibility and leverage new features. Its key differentiators include robust caching mechanisms (including `cacheFile` for cross-restart caching), extensive preprocessing and postprocessing hooks (`preprocess.less`, `postprocess.css`), and fine-grained control over rendering options, making it suitable for both development and production environments by reducing disk I/O.

http-networking web-framework

npm install less-middleware

github ↗package ↗

INSTALL

IMPORT

SIG · LESS-MIDDLEWARE

less-middleware

http-networkingjavascriptv3.1.0

Install

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Import

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Disk

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Pass rate

0/ 6

Env Coverage0 / 6

glibc

18–22

musl

18–22

Install & Compatibility

Where this runs

tested against v? · npm install

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

node 18–226 runs

build_error

glibc

node 18–226 runs

build_error

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

lessMiddleware

✓ import lessMiddleware from 'less-middleware'; // For ESM-compatible setups

✗ import { lessMiddleware } from 'less-middleware';

While CommonJS `require` is shown in the README, modern Node.js projects often use ESM. The package itself likely provides a default export, so `import lessMiddleware from 'less-middleware';` is the correct ESM approach. For Node.js < 12 or CommonJS modules, use `const lessMiddleware = require('less-middleware');`.

lessMiddleware

✓ const lessMiddleware = require('less-middleware');

This is the classic CommonJS import pattern shown in the official documentation and suitable for most Node.js applications that are not pure ESM.

This Express.js quickstart demonstrates how to integrate `less-middleware` to compile LESS files on the fly. It sets up the middleware to serve static files, enabling LESS compilation in a 'public' directory with different caching strategies for development and production environments, and basic Less rendering options like compression.

import express from 'express'; import lessMiddleware from 'less-middleware'; import { fileURLToPath } from 'url'; import { dirname, join } from 'path'; const __filename = fileURLToPath(import.meta.url); const __dirname = dirname(__filename); const app = express(); const publicPath = join(__dirname, 'public'); // Imagine a 'public' directory containing 'styles.less' // app.use(lessMiddleware('/less', { source: join(publicPath, 'less'), dest: join(publicPath, 'css') })); // Basic usage: LESS files in /public will be compiled to /public app.use(lessMiddleware(publicPath, { debug: process.env.NODE_ENV !== 'production', force: process.env.NODE_ENV !== 'production', // Recompile on each request in dev once: process.env.NODE_ENV === 'production', // Recompile once per server restart in prod render: { compress: process.env.NODE_ENV === 'production' } })); app.use(express.static(publicPath)); const port = process.env.PORT || 3000; app.listen(port, () => { console.log(`Server running at http://localhost:${port}`); console.log(`LESS files in ${publicPath} will be compiled and served.`); console.log(`Try creating a 'styles.less' in ${publicPath} and access '/styles.css'`); });

Debug

Known issues

breakingVersion 3.0.0 upgraded Less to version 3.x. This introduced potential breaking changes due to Less.js's own major version update, especially regarding syntax and features removed or altered in Less 3.

fix

Review the Less.js 3.x changelog for any changes that might affect your .less files. Ensure your Less syntax is compatible with Less 3.

affects: >=3.0.0

breakingVersion 2.0.0 introduced significant breaking changes due to an update to Less 2.4. The `options.parser` property was removed, and rendering options are now passed directly via `options.render`.

fix

Replace any usage of `options.parser` with `options.render` for passing rendering-specific options. Consult the less-middleware 2.x README for the new options structure.

affects: >=2.0.0 <3.0.0

gotchaIncorrect configuration of `dest` or `pathRoot` can lead to compiled CSS files not being found or written to unexpected locations. If `dest` is not specified, it defaults to the `source` directory, which may not be desirable in production for separation of concerns.

fix

Always explicitly define `dest` to a desired output directory, especially if source LESS files are not in the same directory where compiled CSS should reside. Ensure `pathRoot` is correctly set if your source and destination directories share a common, non-root parent.

affects: >=1.0.0

gotchaCaching behavior (`force`, `once`, `cacheFile`) requires careful consideration for both development and production. In development, `force: true` is often desired for immediate feedback on style changes, but in production, `once: true` or `cacheFile` for faster startup is critical. Misconfiguration can lead to slow rebuilds or outdated CSS being served.

fix

For development, set `force: true` and `debug: true`. For production, set `once: true` and consider using `cacheFile` to persist import dependency information across server restarts. Ensure `process.env.NODE_ENV` is correctly set for conditional logic.

affects: >=1.0.4

Errors

Common errors & fixes

Error: .less file could not be found or processed.

The middleware could not locate the specified .less source file or an imported .less file.

fix

Verify the `source` option points to the correct directory containing your .less files. Check file paths, capitalization, and ensure read permissions. Use `debug: true` in options for more verbose logging about file resolution.

TypeError: app.use is not a function

This error indicates that `app` is not an Express/Connect application instance, or `app.use` is being called before `app` is properly initialized.

fix

Ensure you have correctly initialized your Express or Connect application, e.g., `const express = require('express'); const app = express();` before calling `app.use(lessMiddleware(...));`.

Error: 'less' not found. Is it installed?

The `less` package, which is a peer/runtime dependency, is not installed in your project.

fix

Install the `less` package: `npm install less --save`. Ensure its version is compatible with your `less-middleware` version.

Upgrade

Version history

3.1.0latest on npm

Audit

Dependencies

lessrequiredCore dependency for LESS compilation. Middleware versions track Less.js major versions.

Agent activity

4 hits · last 30 days

node

Resources

githubhttps://github.com/emberfeather/less.js-middleware ↗

packagehttps://www.npmjs.com/package/less-middleware ↗