karma-esbuild-next

1.1.0 verified Fri May 01 auth: no javascript

An esbuild preprocessor for the Karma test runner, forked from karma-esbuild. It leverages esbuild for fast compilation and readable output, supporting custom esbuild configurations, plugin integration, and single-bundle mode to merge test files into one bundle. Current version 1.1.0 requires esbuild >=0.17.0. Compared to alternatives like karma-webpack or karma-rollup, it offers significantly faster build times due to esbuild's speed, while maintaining compatibility with Karma's standard preprocessor interface.

Common errors

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

cause Missing 'esbuild' in preprocessors array incorrectly, or plugin not installed

fix

Ensure you have added 'karma-esbuild-next' to plugins array in karma.conf.js

error Error: Cannot find module 'karma-esbuild-next' ↓

cause Package not installed or not listed in package.json devDependencies

fix

Run 'npm install --save-dev karma-esbuild-next'

error Error: esbuild: Unexpected option: bundle ↓

cause Using esbuild 'bundle' option inside esbuild config block in karma.conf.js

fix

Use 'singleBundle' instead of 'bundle' for Karma-specific bundling

Warnings

gotcha Preprocessor name must be 'esbuild', not the package name ↓

fix Use 'esbuild' in preprocessors array, not 'karma-esbuild-next'

breaking Requires esbuild >=0.17.0; older versions may fail ↓

fix Update esbuild to version 0.17.0 or later

gotcha singleBundle defaults to true; all test files are bundled into one. This can cause issues if tests rely on separate scopes for globals. ↓

fix Set singleBundle: false if you need separate bundles per test file

deprecated The original karma-esbuild package is unmaintained; this fork is the recommended alternative ↓

fix Switch to karma-esbuild-next

Install

npm install karma-esbuild-next

yarn add karma-esbuild-next

pnpm add karma-esbuild-next

Imports

karma-esbuild-next
wrong
```
npm install --save-dev karma-esbuild
```
correct
```
npm install --save-dev karma-esbuild-next
```
Install the package, then configure in karma.conf.js
config.set({ preprocessors: { "test/**/*.test.js": ["esbuild"] } })
wrong
```
preprocessors: { "test/**/*.test.js": ["karma-esbuild-next"] }
```
correct
```
preprocessors: { "test/**/*.test.js": ["esbuild"] }
```
The preprocessor name is 'esbuild', not the package name
esbuild config block
wrong
```
config.set({ esbuild: { bundle: true } })
```
correct
```
config.set({ esbuild: { define: {}, plugins: [], singleBundle: true } })
```
Use 'singleBundle' for bundling test files; 'bundle' is an esbuild option but not directly supported

Quickstart

Configure Karma to use esbuild preprocessor with Mocha, a define variable, and single bundle mode.

// karma.conf.js
module.exports = function (config) {
  config.set({
    frameworks: ['mocha'],
    files: ['test/**/*.test.js'],
    preprocessors: {
      'test/**/*.test.js': ['esbuild']
    },
    plugins: [
      'karma-esbuild-next'
    ],
    esbuild: {
      define: {
        'process.env.NODE_ENV': JSON.stringify('test')
      },
      singleBundle: true
    },
    browsers: ['ChromeHeadless'],
    singleRun: true
  });
};