node.js require() cache - possible to invalidate?

Question

From the node.js documentation:

Modules are cached after the first time they are loaded. This means (among other things) that every call to require(\'

Answer 1

I couldn't neatly add code in an answer's comment. But I would use @Ben Barkay's answer then add this to the require.uncache function.

    // see https://github.com/joyent/node/issues/8266
    // use in it in @Ben Barkay's require.uncache function or along with it. whatever
    Object.keys(module.constructor._pathCache).forEach(function(cacheKey) {
        if ( cacheKey.indexOf(moduleName) > -1 ) {
            delete module.constructor._pathCache[ cacheKey ];
        }
    }); 

Say you've required a module, then uninstalled it, then reinstalled the same module but used a different version that has a different main script in its package.json, the next require will fail because that main script does not exists because it's cached in Module._pathCache

Answer 2

You can always safely delete an entry in require.cache without a problem, even when there are circular dependencies. Because when you delete, you just delete a reference to the cached module object, not the module object itself, the module object will not be GCed because in case of circular dependencies, there is still a object referencing this module object.

Suppose you have:

script a.js:

var b=require('./b.js').b;
exports.a='a from a.js';
exports.b=b;

and script b.js:

var a=require('./a.js').a;
exports.b='b from b.js';
exports.a=a;

when you do:

var a=require('./a.js')
var b=require('./b.js')

you will get:

> a
{ a: 'a from a.js', b: 'b from b.js' }
> b
{ b: 'b from b.js', a: undefined }

now if you edit your b.js:

var a=require('./a.js').a;
exports.b='b from b.js. changed value';
exports.a=a;

and do:

delete require.cache[require.resolve('./b.js')]
b=require('./b.js')

you will get:

> a
{ a: 'a from a.js', b: 'b from b.js' }
> b
{ b: 'b from b.js. changed value',
  a: 'a from a.js' }

===

The above is valid if directly running node.js. However, if using tools that have their own module caching system, such as jest, the correct statement would be:

jest.resetModules();

Answer 3

Yes, you can invalidate cache.

The cache is stored in an object called require.cache which you can access directly according to filenames (e.g. - /projects/app/home/index.js as opposed to ./home which you would use in a require('./home') statement).

delete require.cache['/projects/app/home/index.js'];

Our team has found the following module useful. To invalidate certain groups of modules.

https://www.npmjs.com/package/node-resource

Answer 4

requireUncached with relative path:

Answer 5

For anyone coming across this who is using Jest, because Jest does its own module caching, there's a built-in function for this - just make sure jest.resetModules runs eg. after each of your tests:

afterEach( function() {
  jest.resetModules();
});

Found this after trying to use decache like another answer suggested. Thanks to Anthony Garvan.

Function documentation here.

Answer 6

Yes, you can access the cache via require.cache[moduleName] where moduleName is the name of the module you wish to access. Deleting an entry by calling delete require.cache[moduleName] will cause require to load the actual file.

This is how you would remove all cached files associated with the module:

/**
 * Removes a module from the cache
 */
function purgeCache(moduleName) {
    // Traverse the cache looking for the files
    // loaded by the specified module name
    searchCache(moduleName, function (mod) {
        delete require.cache[mod.id];
    });

    // Remove cached paths to the module.
    // Thanks to @bentael for pointing this out.
    Object.keys(module.constructor._pathCache).forEach(function(cacheKey) {
        if (cacheKey.indexOf(moduleName)>0) {
            delete module.constructor._pathCache[cacheKey];
        }
    });
};

/**
 * Traverses the cache to search for all the cached
 * files of the specified module name
 */
function searchCache(moduleName, callback) {
    // Resolve the module identified by the specified name
    var mod = require.resolve(moduleName);

    // Check if the module has been resolved and found within
    // the cache
    if (mod && ((mod = require.cache[mod]) !== undefined)) {
        // Recursively go over the results
        (function traverse(mod) {
            // Go over each of the module's children and
            // traverse them
            mod.children.forEach(function (child) {
                traverse(child);
            });

            // Call the specified callback providing the
            // found cached module
            callback(mod);
        }(mod));
    }
};

Usage would be:

// Load the package
var mypackage = require('./mypackage');

// Purge the package from cache
purgeCache('./mypackage');

Since this code uses the same resolver require does, just specify whatever you would for require.

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"Unix was not designed to stop its users from doing stupid things, as that would also stop them from doing clever things." – Doug Gwyn

I think that there should have been a way for performing an explicit uncached module loading.