node-hook

What is node-hook?

The node-hook package allows you to hook into Node.js' require function to modify the behavior of module loading. This can be useful for tasks such as transpiling code on the fly, mocking modules for testing, or adding custom behavior to module loading.

What are node-hook's main functionalities?

Transpile Code on the Fly

This feature allows you to transpile ES6 code to ES5 on the fly using Babel. By hooking into the '.js' extension, you can transform the source code before it is executed.

const hook = require('node-hook');
const babel = require('@babel/core');

hook.hook('.js', (source, filename) => {
  const result = babel.transformSync(source, { filename });
  return result.code;
});

require('./your-es6-file');

Mocking Modules for Testing

This feature allows you to mock specific modules for testing purposes. By checking the filename, you can return a mocked version of the module.

const hook = require('node-hook');

hook.hook('.js', (source, filename) => {
  if (filename.endsWith('some-module.js')) {
    return 'module.exports = { mockedFunction: () => "mocked" };';
  }
  return source;
});

const someModule = require('./some-module');
console.log(someModule.mockedFunction()); // Outputs: mocked

Custom Behavior for Module Loading

This feature allows you to add custom behavior to the module loading process. In this example, it logs the filename of each module being loaded.

const hook = require('node-hook');

hook.hook('.js', (source, filename) => {
  console.log(`Loading module: ${filename}`);
  return source;
});

require('./your-module');

Other packages similar to node-hook

pirates

The pirates package provides a similar functionality to node-hook by allowing you to hook into Node.js' require function. It is often used for transpiling code on the fly or adding custom behavior to module loading. Pirates is more focused on providing a simple and flexible API for hooking into the require function.

proxyquire

Proxyquire allows you to override dependencies during testing without modifying the original code. It is particularly useful for mocking modules in unit tests. Unlike node-hook, which hooks into the require function globally, proxyquire allows you to override dependencies on a per-require basis.

babel-register

Babel-register is a package that hooks into Node.js' require function to transpile ES6/ES7 code on the fly using Babel. It is specifically designed for transpiling code and is often used in development environments. Unlike node-hook, which can be used for various custom behaviors, babel-register is focused solely on code transpilation.

README

node-hook

Run source transform function on Node require

Install and use

npm install --save node-hook

Before loading desired .js files, install hook

var hook = require('node-hook');

function logLoadedFilename(source, filename) {
    return 'console.log("' + filename + '");\n' + source;
}
hook.hook('.js', logLoadedFilename);
require('./dummy');
// prints fulle dummy.js filename, runs dummy.js

hook.unhook('.js'); // removes your own transform

remember: Nodejs caches compiled modules, so if the transform is not working, you might need to delete the cached entry in require.cache, then call require(filename) again to force reload.

Related: Node require replacement really-need.

You can hook several transformers thanks to the code submitted by djulien

Existing transform

You can get the current transform and run any source through it. For example to see how the current source looks when loaded but before evaluated

const filename = resolve('./call-foo.js')
const transform = Module._extensions['.js']
const fakeModule = {
  _compile: source => {
    console.log('transformed code')
    console.log(source)
  }
}
transform(fakeModule, filename)

Small print

Author: Gleb Bahmutov © 2013

• Changelog
• @bahmutov
• glebbahmutov.com
• blog

License: MIT - do anything with the code, but don't blame me if it does not work.

Support: if you find any problems with this module, email / tweet / open issue on Github