istanbul-lib-hook

What is istanbul-lib-hook?

The 'istanbul-lib-hook' package is part of the Istanbul code coverage tool suite. It provides utilities to hook into JavaScript code execution, allowing you to intercept and modify code at runtime. This is particularly useful for code coverage analysis, where you need to track which parts of your code are being executed during tests.

What are istanbul-lib-hook's main functionalities?

Hooking into require

This feature allows you to hook into the Node.js require function. You can specify a matcher function to determine which files to hook into and a transformer function to modify the code of those files before they are executed.

const hook = require('istanbul-lib-hook');
const matcher = (file) => file.endsWith('.js');
const transformer = (code, { filename }) => {
  // Modify the code here
  return code;
};

hook.hookRequire(matcher, transformer);

Hooking into vm.runInThisContext

This feature allows you to hook into the vm.runInThisContext function. Similar to hooking into require, you can specify a matcher and a transformer to modify the code before it is executed in the current context.

const hook = require('istanbul-lib-hook');
const matcher = (file) => file.endsWith('.js');
const transformer = (code, { filename }) => {
  // Modify the code here
  return code;
};

hook.hookRunInThisContext(matcher, transformer);

Unhooking

This feature allows you to unhook from the require or vm.runInThisContext functions. This is useful for cleaning up and restoring the original behavior after you are done with your modifications.

const hook = require('istanbul-lib-hook');

// Hook into require
const matcher = (file) => file.endsWith('.js');
const transformer = (code, { filename }) => {
  // Modify the code here
  return code;
};

const unhook = hook.hookRequire(matcher, transformer);

// Later, unhook
unhook();

Other packages similar to istanbul-lib-hook

proxyquire

Proxyquire is a package that allows you to override dependencies during testing. It provides similar functionality to 'istanbul-lib-hook' in that it allows you to intercept and modify module loading, but it is more focused on dependency injection for testing purposes rather than code coverage.

rewire

Rewire is another package that allows you to modify the behavior of modules during testing. It provides a way to inject mocks and stubs into modules, similar to 'istanbul-lib-hook', but it is more focused on testing and mocking rather than code coverage.

README

istanbul-lib-hook

Hooks for require, vm and script used in istanbul