karma-sourcemap-loader

0.4.0 verified Sat Apr 25 auth: no javascript

A Karma plugin preprocessor that loads existing JavaScript source map files (both inline and external) into the Karma test runner. Version 0.4.0 is current stable. Unlike karma-sourcemap-preprocessor, this plugin does not generate source maps but locates them from previous build steps (e.g., TypeScript, Babel, webpack). It supports remapping source paths via prefix replacement or custom callback, and modifying sourceRoot. Inline source maps using base64 are also supported. Release cadence is low, primarily maintenance updates. Key differentiator: solves source map loading when compilation happens outside Karma.

Common errors

error Error: No provider for "sourcemap"! (Resolving: sourcemap) ↓

cause Preprocessor name 'sourcemap' is misspelled or not configured correctly.

fix

Ensure preprocessors config uses 'sourcemap' exactly, e.g., preprocessors: { '**/*.js': ['sourcemap'] }.

error ReferenceError: module is not defined in ES module scope ↓

cause Using CommonJS module.exports in an ESM project (package.json type: module).

fix

Rename file to .cjs or use export default or dynamic import() for ES modules.

Warnings

gotcha Preprocessor name is 'sourcemap' not 'karma-sourcemap-loader'. ↓

fix Use 'sourcemap' as the preprocessor name in preprocessors config.

gotcha Configuration key is 'sourceMapLoader' (camelCase) not 'sourcemaploader' or 'source-map-loader'. ↓

fix Use 'sourceMapLoader' in config.set().

breaking Removed Node.js < 10 support. Graceful-fs usage may break on older Node. ↓

fix Upgrade Node.js to version 10 or later.

deprecated The 'remapSource' callback function may be deprecated in future versions; prefer 'remapPrefixes'. ↓

fix Use 'remapPrefixes' object instead of 'remapSource' function if possible.

Install

npm install karma-sourcemap-loader

yarn add karma-sourcemap-loader

pnpm add karma-sourcemap-loader

Imports

sourcemap

wrong

preprocessors: { '**/*.js': ['karma-sourcemap-loader'] }

correct

preprocessors: { '**/*.js': ['sourcemap'] }

The preprocessor name is 'sourcemap', not the package name.

sourceMapLoader
wrong
```
config.set({ sourcemapLoader: { ... } })
```
correct
```
config.set({ sourceMapLoader: { ... } })
```
Configuration key must use camelCase: sourceMapLoader (capital M) in karma.conf.js.

remapPrefixes

wrong

sourceMapLoader: { remap: { '/myproject/': '../src/' } }

correct

sourceMapLoader: { remapPrefixes: { '/myproject/': '../src/' } }

The exact key is 'remapPrefixes', not 'remap' or 'prefixes'.

Quickstart

Configures Karma to load existing source maps for all JS files, remapping paths with a prefix.

// karma.conf.js
module.exports = function(config) {
  config.set({
    basePath: '',
    frameworks: ['jasmine'],
    files: ['src/**/*.js', 'test/**/*.spec.js'],
    preprocessors: {
      '**/*.js': ['sourcemap']
    },
    sourceMapLoader: {
      remapPrefixes: {
        '/myproject/': '../src/'
      }
    },
    browsers: ['ChromeHeadless'],
    singleRun: true
  });
};