bttmly / intercept-require

intercept require() calls

intercept-require

Installation

npm install intercept-require

About

Intercept, prevent, modify, and short-circuit calls to require(). Given that this involves messing with the methods Node.js uses to require modules, it should be used judiciously. A few possible use-cases:

• You're deprecating use of a library you don't control; use this module to print a deprecation warning and a stack trace whenever that library is require'd

• Transparently stubbing dependencies. Sure, dependency injection is probably a better pattern, but it can be verbose. Instead, you could (during testing) replace e.g. redis with a simple in-memory store that exposes the same interface.

• Implementing some kind of development environment hot-swapping functionality that wraps modules in a Proxy and transparently reloads them when files change

... and any other bad ideas you can think up!

Example

const intercept = require("intercept-require");
// in this example, just transparently log every require
const restore = intercept(function (moduleExport, info) {
  // moduleExport is whatever the actual module exported

  // info looks like:
  //  {
  //    moduleId: "lodash",
  //    callingFile: "index.js",
  //    native: false,
  //    extname: ".js",
  //    thirdParty: true,
  //    exports: [[actual lodash object]]
  //    absPath: /from/root/to/project/node_modules/lodash/lodash.js,
  //    absPathResolvedCorrectly: true,
  //    testOnly: false,
  //    local: false
  //  }
  console.log("require:", info.moduleId, "from", info.callingFile);

  // value returned from this function will be passed back to the caller as if it was module.exports
  return moduleExport;
}, config);
// config has only one option `shortCircuit: boolean`
// if short-circuit is active, `moduleExport` argument to listener will be null

// require() calls now being intercepted
restore();
// require() calls no longer intercepted