Istanbul

What Istanbul is

Istanbul is an open-source JavaScript coverage tool that instruments code with counters, showing how tests exercise a project. It handles ES5 and ES2015+ JavaScript, with first-class ES6 and later support through babel-plugin-istanbul. Coverage includes lines, statements, functions, and branches. Reports can be emitted as terminal text, HTML, or lcov output, with reporters supplied directly or through npm packages. The nyc command-line interface supports subprocess instrumentation and works with most JavaScript test frameworks, including tap, mocha, and AVA. Listed integrations include nyc, c8, Jest, and node-tap; c8 uses Istanbul reports for V8 coverage. Source-mapped coverage is listed for Babel and TypeScript projects. Coverage gates are supported, but pull-request annotations are not. Istanbul can be installed as a development dependency and run before a mocha command. Advanced documentation covers source instrumentation, process trees, __coverage__ reports, and alternative reporters. The project uses the Revised BSD License.