loader-runner

library4.3.2jsnpmunverified

Runs (webpack) loaders as an independent module without webpack itself. Current stable version is 4.3.2, released in 2021 with performance improvements. Minimal release cadence: roughly one version per year. Key differentiator: it allows running loaders in isolation for testing or custom build pipelines. Supports Node.js >=6.11.5 and is ESM/CJS compatible. Lightweight, focuses solely on loader execution logic with hooks for resource processing.

testing devops

npm install loader-runner

github ↗package ↗

INSTALL

IMPORT

SIG · LOADER-RUNNER

loader-runner

testingjavascriptv4.3.2

Install

—

Import

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Disk

—

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.

runLoaders

✓ import { runLoaders } from 'loader-runner'

✗ const runLoaders = require('loader-runner')

Default import is not available; use named import. CommonJS works with require('loader-runner').runLoaders, but named import is preferred for ESM.

runLoaders

✓ const { runLoaders } = require('loader-runner')

✗ const runLoaders = require('loader-runner').default

Destructuring from require is correct. There is no default export.

type LoaderDefinition

✓ import type { LoaderDefinition } from 'loader-runner'

LoaderDefinition is a TypeScript type exported for loader implementations. Use with 'import type' for type-only usage.

Demonstrates basic usage of runLoaders with a resource, loader configuration, and a callback.

import { runLoaders } from 'loader-runner'; import { readFile } from 'fs'; runLoaders({ resource: '/path/to/file.txt?query', loaders: [ { loader: '/path/to/loader.js', options: { minimize: true } } ], context: {}, readResource: readFile }, (err, result) => { if (err) { console.error(err); return; } console.log(result.result[0].toString()); console.log(result.fileDependencies); });

Debug

Known issues

breakingSince v3, the minimum Node.js version is 6.

fix

Upgrade Node.js to >=6 or stick to v2 if using older Node.

affects: >=3.0.0

breakingSince v3, callback can accept undefined as 'no result' in pitching phase, and errors are reported via callback instead of throwing.

fix

Update loader code to handle callback(err, undefined) and avoid throwing.

affects: >=3.0.0

deprecatedThe old approach of using System.import for loader loading was removed in v3.

fix

Use normal require/import for loaders.

affects: >=3.0.0

gotchaThe callback may be called twice with a rejected promise if the loader returns a promise that rejects after the callback is already invoked.

fix

Ensure loaders do not call both callback and reject a promise; favor one error handling mechanism.

affects: >=2.4.0

gotchaAlways set resourcePath, resourceQuery and resourceHash to empty string when request is empty (since v4.3.1).

fix

If relying on these properties, check that they are empty strings instead of undefined.

affects: >=4.3.1

gotchaResource string with '#' must be escaped to avoid misinterpretation (since v4.1.0).

fix

Use escape sequences for '#' in resource and loader requests.

affects: >=4.1.0

Errors

Common errors & fixes

Cannot find module 'loader-runner'

Package not installed or incorrect import path.

fix

Run 'npm install loader-runner' and use correct import: 'import { runLoaders } from "loader-runner"'.

runLoaders is not a function

Wrong import style — default import used instead of named import.

fix

Change import to: 'import { runLoaders } from "loader-runner"' or use CommonJS destructuring: 'const { runLoaders } = require("loader-runner")'.

Callback called twice with rejected promise

Loader returns a promise that rejects after calling callback.

fix

Remove callback call when using promise; use only promise resolve/reject.

TypeError: Cannot read property 'result' of undefined

Error occurred but err is null in callback if result is undefined.

fix

Check both err and result in callback; result may be undefined on error.

Upgrade

Version history

4.3.2latest on npm

Audit

Dependencies

No dependency data recorded yet.

Agent activity

2 hits · last 30 days

node

Resources

githubhttps://github.com/webpack/loader-runner ↗

packagehttps://www.npmjs.com/package/loader-runner ↗