VehicleMonitor-WEB/node_modules/stealthy-require

Stealthy-Require

This is probably the closest you can currently get to require something in node.js with completely bypassing the require cache.

stealthy-require works like this:

1. It clears the require cache.
2. It calls a callback in which you require your module(s) without the cache kicking in.
3. It clears the cache again and restores its old state.

The restrictions are:

• Native modules cannot be required twice. Thus this module bypasses the require cache only for non-native (e.g. JS) modules.
• The require cache is only bypassed for all operations that happen synchronously when a module is required. If a module lazy loads another module at a later time that require call will not bypass the cache anymore.

This means you should have a close look at all internal require calls before you decide to use this library.

Installation

This is a module for node.js and is installed via npm:

npm install stealthy-require --save

Usage

Let's say you want to bypass the require cache for this require call:

var request = require('request');

With stealthy-require you can do that like this:

var stealthyRequire = require('stealthy-require');

var requestFresh = stealthyRequire(require.cache, function () {
    return require('request');
});

The require cache is bypassed for the module you require (i.e. request) as well as all modules the module requires (i.e. http and many more).

Sometimes the require cache shall not be bypassed for specific modules. E.g. request is required but tough-cookie – on which request depends on – shall be required using the regular cache. For that you can pass two extra arguments to stealthyRequire(...):

• A callback that requires the modules that shall be required without bypassing the cache
• The module variable

var stealthyRequire = require('stealthy-require');

var requestFresh = stealthyRequire(require.cache, function () {
    return require('request');
},
function () {
    require('tough-cookie'); // No return needed
    // You can require multiple modules here
}, module);

Usage with Module Bundlers

• Webpack works out-of-the-box like described in the Usage section above.
• Browserify does not expose require.cache. However, as of browserify@13.0.1 the cache is passed as the 6th argument to CommonJS modules. Thus you can pass this argument instead:

// Tweak for Browserify - using arguments[5] instead of require.cache
var requestFresh = stealthyRequire(arguments[5], function () {
    return require('request');
});

Preventing a Memory Leak When Repeatedly Requiring Fresh Module Instances in Node.js

If you are using stealthy-require in node.js and repeatedly require fresh module instances the module.children array will hold all module instances which prevents unneeded instances to be garbage collected.

Assume your code calls doSomething() repeatedly.

var stealthyRequire = require('stealthy-require');

function doSomething() {

    var freshInstance = stealthyRequire(require.cache, function () {
        return require('some-module');
    });
    
    return freshInstance.calc();

}

After doSomething() returns freshInstance is not used anymore but won’t be garbage collected because module.children still holds a reference. The solution is to truncate module.children accordingly:

var stealthyRequire = require('stealthy-require');

function doSomething() {

    var initialChildren = module.children.slice(); // Creates a shallow copy of the array

    var freshInstance = stealthyRequire(require.cache, function () {
        return require('some-module');
    });

    module.children = initialChildren;

    return freshInstance.calc();

}

The slice operation removes all new module.children entries created during the stealthyRequire(...) call and thus freshInstance gets garbage collected after doSomething() returns.

Technical Walkthrough

// 1. Load stealthy-require
var stealthyRequire = require('stealthy-require');
// This does nothing but loading the code.
// It has no side-effects like patching the module loader or anything.

// Any regular require works as always.
var request1 = require('request');

// 2. Call stealthyRequire with passing the require cache and a callback.
var requestFresh = stealthyRequire(require.cache, function () {

    // 2a. Before this callback gets called the require cache is cleared.

    // 2b. Any require taking place here takes place on a clean require cache.
    // Since the require call is part of the user's code it also works with module bundlers.
    return require('request');
    // Anything returned here will be returned by stealthyRequire(...).

    // 2c. After this callback gets called the require cache is
    // - cleared again and
    // - restored to its old state before step 2.

});

// Any regular require again works as always.
// In this case require returns the cached request module instance.
var request2 = require('request');

// And voilà:
request1 === request2 // -> true
request1 === requestFresh // -> false

Contributing

To set up your development environment for stealthy-require:

1. Clone this repo to your desktop,
2. in the shell cd to the main folder,
3. hit npm install,
4. hit npm install gulp -g if you haven't installed gulp globally yet, and
5. run gulp dev. (Or run node ./node_modules/.bin/gulp dev if you don't want to install gulp globally.)

gulp dev watches all source files and if you save some changes it will lint the code and execute all tests. The test coverage report can be viewed from ./coverage/lcov-report/index.html.

If you want to debug a test you should use gulp test-without-coverage to run all tests without obscuring the code by the test coverage instrumentation.

Change History

• v1.1.1 (2017-05-08)
  • Fix that stops undefined entries from appearing in require.cache (Thanks to @jasperjn from reporting this in issue #4)
• v1.1.0 (2017-04-25)
  • Added ability to disable bypassing the cache for certain modules (Thanks to @novemberborn for suggesting this in issue #3)
  • Added section in README about a potential memory leak (Thanks to @Flarna and @novemberborn for bringing that up in issue #2)
  • Performance optimizations (Thanks to @jcready for pull request #1)
• v1.0.0 (2016-07-18)
  • Breaking Change: API completely changed. Please read the Usage section again.
  • Redesigned library to support module bundlers like Webpack and Browserify
• v0.1.0 (2016-05-26)
  • Initial version

License (ISC)

In case you never heard about the ISC license it is functionally equivalent to the MIT license.

See the LICENSE file for details.