What is require-in-the-middle?
The require-in-the-middle package allows for the interception and modification of Node.js module loading. This can be particularly useful for instrumentation, logging, or modifying module behavior at runtime without altering the original module code.
What are require-in-the-middle's main functionalities?
Intercepting module loading
This feature allows you to intercept the loading of specific modules (e.g., 'http') and execute custom logic, such as logging when a module is loaded. The callback function receives the exports of the module, the name of the module, and the base directory.
const hook = require('require-in-the-middle');
hook(['http'], { internals: true }, (exports, name, basedir) => {
console.log(`Module loaded: ${name}`);
return exports;
});
Modifying module exports
This demonstrates how to modify the exports of a module, in this case, 'express'. It wraps the original express function in a new function that logs a message every time it is called before proceeding with the original behavior.
const hook = require('require-in-the-middle');
hook(['express'], (exports, name) => {
const originalFunction = exports;
function modifiedFunction() {
console.log('Express function called');
return originalFunction.apply(this, arguments);
}
return modifiedFunction;
});
Other packages similar to require-in-the-middle
shimmer
Shimmer is a package for wrapping and replacing Node.js module methods. It is similar to require-in-the-middle in its ability to modify module behavior at runtime, but it focuses more on individual method manipulation rather than intercepting module loading.
proxyquire
Proxyquire allows for the overriding of modules during testing by intercepting 'require' calls. It is similar to require-in-the-middle in that it manipulates module loading, but it is specifically designed for testing scenarios, making it easier to mock modules.
require-in-the-middle
Hook into the Node.js require
function. This allows you to modify
modules on-the-fly as they are being required.
Installation
npm install require-in-the-middle --save
Usage
var path = require('path')
var hook = require('require-in-the-middle')
hook(['express', 'mongodb'], function (exports, name, basedir) {
var version = require(path.join(basedir, 'package.json')).version
console.log('loading %s@%s', name, version)
exports._version = version
return exports
})
API
The require-in-the-middle module exposes a single function:
function ([modules, ]onrequire) {}
You can optionally supply an array of module names as the first argument
to limit which modules will trigger a call of the onrequire
callback.
Supply a callback function as the last argument. This function will be
called the first time a module is required. The onrequire
function is
called with three arguments:
exports
- The value of the module.exports
property that would
normally be exposed by the required modulename
- The name of the module being requiredbasedir
- The directory of the where the module is located
Return the value you want the module to expose (normally the exports
argument).
License
MIT