nyc-middleware

library1.0.4jsnpmunverified

Connect/Express middleware for NYC (Istanbul) code coverage in server-side and client-side Node.js applications. Version 1.0.4 is current. Provides hookLoader to instrument server code via require() hooks, createHandler to expose live coverage reports (HTML/JSON/lcov), reset, and download endpoints under /coverage, and createClientHandler to serve instrumented browser JS. Ported from istanbul-middleware to use nyc (istanbul v2). No longer actively maintained; latest release is stable.

testing

npm install nyc-middleware

github ↗package ↗homepage ↗

INSTALL

IMPORT

SIG · NYC-MIDDLEWARE

nyc-middleware

testingjavascriptv1.0.4

harness data pending

Install & Compatibility

Where this runs

No compatibility data collected yet for this library.

Code

Verified usage

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

hookLoader

✓ import { hookLoader } from 'nyc-middleware';

✗ const { hookLoader } = require('nyc-middleware');

ESM or CJS both work; package does not enforce ESM.

createHandler

✓ import { createHandler } from 'nyc-middleware';

✗ const handler = require('nyc-middleware').createHandler;

Preferred named import for clarity.

createClientHandler

✓ import { createClientHandler } from 'nyc-middleware';

✗ const createClientHandler = require('nyc-middleware').createClientHandler;

For browser-side instrumentation.

Sets up NYC middleware coverage on Express: hooks require() and exposes /coverage endpoints.

import express from 'express'; import { hookLoader, createHandler } from 'nyc-middleware'; const app = express(); const isCoverageEnabled = process.env.COVERAGE === 'true'; if (isCoverageEnabled) { console.log('Hooking loader for coverage (not for production!)'); hookLoader(__dirname, { verbose: true }); } // require your modules after hooking import stuff from './lib'; if (isCoverageEnabled) { app.use('/coverage', createHandler()); } app.get('/', (req, res) => res.send('Hello World')); app.listen(3000);

Debug

Known issues

deprecatedPackage is based on istanbul-middleware and uses nyc v1. Use a more modern solution like c8 or @istanbuljs/nyc-config-babel for active projects.

fix

Migrate to c8 (built into Node 14+) or use @istanbuljs/nyc-config-babel directly.

affects: *

gotchahookLoader must be called before any require() calls that load the code to be covered. Otherwise coverage will be missing.

fix

Call hookLoader at the very top of your main entry point before requiring any local modules.

affects: *

gotchaThe createClientHandler for browser coverage only works with simple absolute URLs; frameworks like Angular/React may need custom handling.

fix

Write custom middleware to instrument browser JS or use nyc's built-in instrument command.

affects: *

breakingVersion 1.0.x dropped support for Node <0.10 – but as of 2025 this is not an issue; however, the package may have compatibility issues with modern Node versions (>=14).

fix

Test coverage on your Node version; consider using c8 for native ESM coverage.

affects: >=1.0.0

Errors

Common errors & fixes

Error: Cannot find module 'nyc-middleware'

nyc-middleware is not installed or not in node_modules.

fix

Run: npm install nyc-middleware

TypeError: hookLoader is not a function

Improper import/require; possibly using default import instead of named.

fix

Use: import { hookLoader } from 'nyc-middleware';

ReferenceError: __dirname is not defined

Using ES modules with __dirname; __dirname is not available in ESM.

fix

Use: import { fileURLToPath } from 'url'; const __dirname = fileURLToPath(new URL('.', import.meta.url));

Upgrade

Version history

1.0.4latest on npm

Audit

Dependencies

nycrequiredRequires nyc to be installed in the project as it uses nyc's coverage instrumentation.

expressoptionalDesigned to work with Express/Connect middleware – may need express for createHandler usage.

Agent activity

6 hits · last 30 days

node

Resources

githubssh://git@github.com/uxkjaer/nyc-middleware ↗

packagenyc-middleware ↗

homepagehttps://github.com/uxkjaer/nyc-middleware#readme ↗