istanbul-instrumenter-loader

What is istanbul-instrumenter-loader?

The 'istanbul-instrumenter-loader' is a webpack loader that instruments JavaScript files with Istanbul coverage, which is useful for generating code coverage reports for your tests.

What are istanbul-instrumenter-loader's main functionalities?

Instrumenting JavaScript files

This feature allows you to instrument JavaScript files for code coverage. The code sample shows how to configure webpack to use 'istanbul-instrumenter-loader' for all JavaScript files in the 'src/' directory.

module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        include: path.resolve('src/'),
        loader: 'istanbul-instrumenter-loader',
        options: { esModules: true }
      }
    ]
  }
};

Using with Babel

This feature demonstrates how to use 'istanbul-instrumenter-loader' in conjunction with 'babel-loader' to transpile and instrument JavaScript files. The code sample shows the configuration for webpack to use both loaders.

module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        include: path.resolve('src/'),
        use: [
          'babel-loader',
          {
            loader: 'istanbul-instrumenter-loader',
            options: { esModules: true }
          }
        ]
      }
    ]
  }
};

Other packages similar to istanbul-instrumenter-loader

babel-plugin-istanbul

The 'babel-plugin-istanbul' is a Babel plugin that instruments your code with Istanbul coverage. It is similar to 'istanbul-instrumenter-loader' but is used as a Babel plugin instead of a webpack loader. This can be more convenient if you are already using Babel for transpilation.

nyc

The 'nyc' package is a command-line interface for Istanbul. It provides a more comprehensive solution for code coverage, including running tests and generating reports. Unlike 'istanbul-instrumenter-loader', which is a webpack loader, 'nyc' can be used independently of webpack.

README

Istanbul Instrumenter Loader

Instrument JS files with istanbul-lib-instrument for subsequent code coverage reporting

Install

npm i -D istanbul-instrumenter-loader

Usage

References

• karma-webpack
• karma-coverage-istanbul-reporter

Structure

├─ src
│ |– components
│ | |– bar
│ | │ |─ index.js
│ | |– foo/
│     |– index.js
|– test
| |– src
| | |– components
| | | |– foo
| | | | |– index.js

To create a code coverage report for all components (even for those for which you have no tests yet) you have to require all the 1) sources and 2) tests. Something like it's described in "alternative usage" of karma-webpack

test/index.js

// requires all tests in `project/test/src/components/**/index.js`
const tests = require.context('./src/components/', true, /index\.js$/);

tests.keys().forEach(tests);

// requires all components in `project/src/components/**/index.js`
const components = require.context('../src/components/', true, /index\.js$/);

components.keys().forEach(components);

ℹ️ This file will be the only entry point for karma

karma.conf.js

config.set({
  ...
  files: [
    'test/index.js'
  ],
  preprocessors: {
    'test/index.js': 'webpack'
  },
  webpack: {
    ...
    module: {
      rules: [
        // instrument only testing sources with Istanbul
        {
          test: /\.js$/,
          use: { loader: 'istanbul-instrumenter-loader' },
          include: path.resolve('src/components/')
        }
      ]
    }
    ...
  },
  reporters: [ 'progress', 'coverage-istanbul' ],
  coverageIstanbulReporter: {
    reports: [ 'text-summary' ],
    fixWebpackSourcePaths: true
  }
  ...
});

with Babel

You must run the instrumentation as a post step

webpack.config.js

{
  test: /\.js$|\.jsx$/,
  use: {
    loader: 'istanbul-instrumenter-loader',
    options: { esModules: true }
  },
  enforce: 'post',
  exclude: /node_modules|\.spec\.js$/,
}

Options

The loader supports all options supported by istanbul-lib-instrument

Name	Type	Default	Description
debug	{Boolean}	false	Turn on debugging mode
compact	{Boolean}	true	Generate compact code
autoWrap	{Boolean}	false	Set to true to allow return statements outside of functions
esModules	{Boolean}	false	Set to true to instrument ES2015 Modules
coverageVariable	{String}	__coverage__	Name of global coverage variable
preserveComments	{Boolean}	false	Preserve comments in output
produceSourceMap	{Boolean}	false	Set to true to produce a source map for the instrumented code
sourceMapUrlCallback	{Function}	null	A callback function that is called when a source map URL is found in the original code. This function is called with the source filename and the source map URL

webpack.config.js

{
  test: /\.js$/,
  use: {
    loader: 'istanbul-instrumenter-loader',
    options: {...options}
  }
}

Maintainers

Kir Belevich

Juho Vepsäläinen

Joshua Wiens

Michael Ciniawsky

Matt Lewis