v8-to-istanbul

What is v8-to-istanbul?

The v8-to-istanbul package is a tool that converts V8 coverage information into a format that is compatible with Istanbul's coverage reports. It allows developers to generate coverage reports for JavaScript code executed in the V8 JavaScript engine, which is used by Node.js and Chrome.

What are v8-to-istanbul's main functionalities?

Convert V8 coverage to Istanbul format

This feature allows you to convert V8 coverage information into the Istanbul format. You can then use this data to generate reports with Istanbul-compatible tools.

const v8toIstanbul = require('v8-to-istanbul');
const scriptPath = './path/to/script.js';
const v8Coverage = require('./path/to/v8-coverage.json');

const converter = v8toIstanbul(scriptPath);
converter.load();
converter.applyCoverage(v8Coverage);
const istanbulCoverage = converter.toIstanbul();
console.log(JSON.stringify(istanbulCoverage, null, 2));

Exclude specific functions or lines from coverage

This feature allows you to exclude specific functions or ranges of lines from the coverage report. This is useful for ignoring code that you do not want to include in your coverage metrics.

const v8toIstanbul = require('v8-to-istanbul');
const scriptPath = './path/to/script.js';

const converter = v8toIstanbul(scriptPath, {
  exclude: ['**/node_modules/**', '**/test/**']
});
converter.exclude('functionName');
converter.excludeRange([startLine, endLine]);

Other packages similar to v8-to-istanbul

nyc

nyc is a command-line tool and library for instrumenting code with Istanbul's coverage tracking and reporting. It is a more comprehensive tool that includes v8-to-istanbul's functionality as part of its coverage processing pipeline.

c8

c8 is a higher-level tool that uses v8-to-istanbul under the hood to collect and report V8 code coverage. It provides a simple command-line interface to generate coverage reports without needing to manually convert V8 coverage data.

istanbul-lib-instrument

istanbul-lib-instrument is part of the Istanbul API and is responsible for instrumenting JavaScript code. It differs from v8-to-istanbul in that it modifies the code to track coverage, rather than converting coverage data from the V8 engine.

README

v8-to-istanbul

converts from v8 coverage format to istanbul's coverage format.

Usage

const v8toIstanbul = require('v8-to-istanbul')
// the path to the original source-file is required, as its contents are
// used during the conversion algorithm.
const converter = v8toIstanbul('./path-to-instrumented-file.js')
await converter.load() // this is required due to the async source-map dependency.
// provide an array of coverage information in v8 format.
converter.applyCoverage([
  {
    "functionName": "",
    "ranges": [
      {
        "startOffset": 0,
        "endOffset": 520,
        "count": 1
      }
    ],
    "isBlockCoverage": true
  },
  // ...
])
// output coverage information in a form that can
// be consumed by Istanbul.
console.info(JSON.stringify(converter.toIstanbul()))

// cleanup resources allocated in "load" (i.e. by the source-map dependency),
// the converter may not be used anymore afterwards
converter.destroy() 

Ignoring Uncovered Lines

Sometimes you might find yourself wanting to ignore uncovered lines in your application (for example, perhaps you run your tests in Linux, but there's code that only executes on Windows).

To ignore lines, use the special comment /* c8 ignore next */.

ignoring the next line

const myVariable = 99
/* c8 ignore next */
if (process.platform === 'win32') console.info('hello world')

ignoring the next N lines

const myVariable = 99
/* c8 ignore next 3 */
if (process.platform === 'win32') {
  console.info('hello world')
}

ignoring all lines until told

/* c8 ignore start */
function dontMindMe() {
  // ...
}
/* c8 ignore stop */

ignoring the same line as the comment

const myVariable = 99
const os = process.platform === 'darwin' ? 'OSXy' /* c8 ignore next */ : 'Windowsy' 

Testing

To execute tests, simply run:

npm test