Related
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('foo') will get exactly the same object returned, if it would resolve to the same file.
Is there a way to invalidate this cache? i.e. for unit testing, I'd like each test to be working on a fresh object.
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();
If you always want to reload your module, you could add this function:
function requireUncached(module) {
delete require.cache[require.resolve(module)];
return require(module);
}
and then use requireUncached('./myModule') instead of require.
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.
"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.
There's a Simple Module for that (with tests)
We had this exact issue while testing our code (delete cached modules so they can be re-required in a fresh state) so we reviewed all the suggestions of people on the various StackOverflow Questions & Answers and put together a simple node.js module (with tests):
https://www.npmjs.com/package/decache
As you would expect, works for both published npm packages and locally defined modules. Windows, Mac, Linux, etc.
How? (usage)
Usage is pretty simple:
install
Install the module from npm:
npm install decache --save-dev
Use it in your code:
// require the decache module:
const decache = require('decache');
// require a module that you wrote"
let mymod = require('./mymodule.js');
// use your module the way you need to:
console.log(mymod.count()); // 0 (the initial state for our counter is zero)
console.log(mymod.incrementRunCount()); // 1
// delete the cached module:
decache('./mymodule.js');
//
mymod = require('./mymodule.js'); // fresh start
console.log(mymod.count()); // 0 (back to initial state ... zero)
If you have any questions or need more examples, please create a GitHub issue:
https://github.com/dwyl/decache/issues
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.
The solutions is to use:
delete require.cache[require.resolve(<path of your script>)]
Find here some basic explanations for those who, like me, are a bit new in this:
Suppose you have a dummy example.js file in the root of your directory:
exports.message = "hi";
exports.say = function () {
console.log(message);
}
Then you require() like this:
$ node
> require('./example.js')
{ message: 'hi', say: [Function] }
If you then add a line like this to example.js:
exports.message = "hi";
exports.say = function () {
console.log(message);
}
exports.farewell = "bye!"; // this line is added later on
And continue in the console, the module is not updated:
> require('./example.js')
{ message: 'hi', say: [Function] }
That's when you can use delete require.cache[require.resolve()] indicated in luff's answer:
> delete require.cache[require.resolve('./example.js')]
true
> require('./example.js')
{ message: 'hi', say: [Function], farewell: 'bye!' }
So the cache is cleaned and the require() captures the content of the file again, loading all the current values.
rewire is great for this use case, you get a new instance with each call. Easy dependency injection for node.js unit testing.
rewire adds a special setter and getter to modules so you can modify their behaviour for better unit testing. You may
inject mocks for other modules or globals like process
leak private variables
override variables within the module.
rewire does not load the file and eval the contents to emulate node's require mechanism. In fact it uses node's own require to load the module. Thus your module behaves exactly the same in your test environment as under regular circumstances (except your modifications).
Good news to all caffeine-addicts: rewire works also with Coffee-Script. Note that in this case CoffeeScript needs to be listed in your devDependencies.
I'd add to luff's answer one more line and change the parameter name:
function requireCached(_module){
var l = module.children.length;
for (var i = 0; i < l; i++)
{
if (module.children[i].id === require.resolve(_module))
{
module.children.splice(i, 1);
break;
}
}
delete require.cache[require.resolve(_module)];
return require(_module)
}
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
I am not 100% certain of what you mean by 'invalidate', but you can add the following above the require statements to clear the cache:
Object.keys(require.cache).forEach(function(key) { delete require.cache[key] })
Taken from #Dancrumb's comment here
requireUncached with relative path: 🔥
const requireUncached = require => module => {
delete require.cache[require.resolve(module)];
return require(module);
};
module.exports = requireUncached;
invoke requireUncached with relative path:
const requireUncached = require('../helpers/require_uncached')(require);
const myModule = requireUncached('./myModule');
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
If you want a module to simply never be cached (sometimes useful for development, but remember to remove it when done!) you can just put delete require.cache[module.id]; inside the module.
here's my version of this answer, which handles not loading a file if it has (for example) syntax errors
function reacquire(module) {
const fullpath = require.resolve(module);
const backup = require.cache[fullpath];
delete require.cache[fullpath];
try {
const newcopy = require(module);
console.log("reqcquired:",module,typeof newcopy);
return newcopy;
} catch (e) {
console.log("Can't reqcquire",module,":",e.message);
require.cache[fullpath] = backup;
return backup;
}
}
Following two step procedure is working perfectly for me.
After changing Model file i-e 'mymodule.js' dynamically, you need to Delete precompiled model in mongoose model first then reload it using require-reload
Example:
// Delete mongoose model
delete mongoose.connection.models[thisObject.singular('mymodule')]
// Reload model
var reload = require('require-reload')(require);
var entityModel = reload('./mymodule.js');
The documentation says:
Modules are cached in this object when they are required. By deleting a key value from this object, the next require will reload the module. This does not apply to native addons, for which reloading will result in an error.
If it's for unit tests, another good tool to use is proxyquire. Everytime you proxyquire the module, it will invalidate the module cache and cache a new one. It also allows you to modify the modules required by the file that you are testing.
I made a small module to delete module from the cache after loading. This forces reevaluation of the module next time it is required. See https://github.com/bahmutov/require-and-forget
// random.js
module.exports = Math.random()
const forget = require('require-and-forget')
const r1 = forget('./random')
const r2 = forget('./random')
// r1 and r2 will be different
// "random.js" will not be stored in the require.cache
PS: you can also put "self-destruct" into the module itself. See https://github.com/bahmutov/unload-me
PSS: more tricks with Node require in my https://glebbahmutov.com/blog/hacking-node-require/
I have a variable named number_of_clusters which must be updated periodically. number_of_clusters must also be shared with other modules to read it. how can I assure that reading modules will read a fresh copy of this variable each time they access that?
I dont want to use database to share this variable so I thought I could share it via process.env
process.env.number_of_clusters = 1;
is it a good practice?
Seems like your searching for a global variable:
global. number_of_clusters = 1
However using a database or a file would probably be a nicer solution.
Try reading/writing in a file?
var fs = require('fs');
fs.writeFile("/path/to/file", "whatever", function(err) {
console.log("The file was saved!");
});
fs.readFile('/path/to/file', 'utf8', function(err, contents) {
console.log(contents); // -> whatever
});
If the other modules are running as part of the same Nodejs process,
you can just export a getter to other modules which will get the fresh value of number_of_clusters for them.
Like:
function get_number_of_clusters() {
return number_of_clusters;
}
module.exports = { get_number_of_clusters };
Now in other modules, you need to import this module and call this method, like:
var getter = require('path/to/above/module').get_number_of_clusters;
var number_of_clusters = getter();
You could use socket.io to store the variable on the server and have it emit to all pages.
I'm creating an npm package called ctgen and I need to reference a folder within that package. Should I hard code the reference to that folder?
e.g. src = './node_modules/ctgen/scaffold'
or is there a pre-made function that will do this for me?
For a bit more clarity on my issue. I have the following function in my package:
var createFile = function (fileName, componentName, doc) {
// Tell the user what is happening
console.log(chalk.blue('\nCreating', fileName, '...'))
// Bring in the scaffold files (note this should point to the scaffold folder in node modules/ctgen)
var scaffold = './scaffold/' + fileName
fs.readFile(scaffold, 'utf8', function (err, data) {
if (err) return console.log(chalk.red(err))
var result = data.replace(/%cname%/g, componentName)
if (doc) {
var d = new Date()
result = result.replace(/%cfname%/g, doc.componentName)
result = result.replace(/%cdesc%/g, doc.componentDesc)
result = result.replace(/%cauthor%/g, doc.userName)
result = result.replace(/%cagithub%/g, doc.userGithub)
result = result.replace(/%creationdate%/g, d.getDate() + '/' + d.getMonth() + '/' + d.getFullYear())
}
fs.writeFile('./src/components/' + componentName + '/' + fileName, result, function (err) {
if (err) return console.log(chalk.red(err))
console.log(chalk.green(fileName, 'created!'))
})
})
}
It looks in a folder called scaffold for the following files:
view.php
style.styl
component.json
It then pulls the file into a cache, performs a find and replace on some strings and then writes the output to a file in the users project.
It seems though that whenever I try to reference the 'scaffold' folder, it's trying to find it in the users project folder and not in my package folder.
I'm very hesitant to reference the scaffold folder by writing '/node_modules/ctgen/scaffold' as that seems like the wrong thing to do to me.
What you want is __dirname.
If I understand your question, you have a ressource folder contained in your module, and have trouble accessing it since the current path is the path of the app, not your module.
__dirname will contain the path of your script file, and so will point to your module file.
I presume your module is named ctgen, and the files you want to access are in ctgen/scaffold. So in your code, try to access __dirname/scaffold.
In short NO. If you want to read more about how node looks for required files pleas read this: https://nodejs.org/dist/latest-v7.x/docs/api/modules.html#modules_addenda_package_manager_tips
if you are creating an npm package, specify your dependent npm modules within your package.json and use them as intended in node (with require('your-dependent-module-name')). After you published your module and someone npm install --save your-module, it will also install your dependencies into [usrDir]/node_modules/[your-module]/node_modules, where your module will find what it needs.
That beeing said; yes, you could reference __dirname + 'node_modules/[something] but that wouldn't be smart as it makes assumptions how the user is using your module. At the same time, node+npm solves this problem for you, so there is no reason for you to want to do this)
I want to use factor-bundle to find common dependencies for my browserify entry points and save them out into a single common bundle:
https://www.npmjs.org/package/factor-bundle
The factor-bundle documentation makes it seem very easy to do on the command line, but I want to do it programmatically and I'm struggling to get my head around it.
My current script is this (I'm using reactify to transform react's jsx files too):
var browserify = require('browserify');
var factor = require('factor-bundle')
var glob = require('glob');
glob('static/js/'/**/*.{js,jsx}', function (err, files) {
var bundle = browserify({
debug: true
});
files.forEach(function(f) {
bundle.add('./' + f);
});
bundle.transform(require('reactify'));
// factor-bundle code goes here?
var dest = fs.createWriteStream('./static/js/build/common.js');
var stream = bundle.bundle().pipe(dest);
});
I'm trying to figure out how to use factor-bundle as a plugin, and specify the desired output file for each of the input files (ie each entry in files)
This answer is pretty late, so it's likely you've either already found a solution or a work around for this question. I'm answering this as it's quite similar to my question.
I was able to get this working by using factor-bundle as a browserify plugin. I haven't tested your specific code, but the pattern should be the same:
var fs = require('fs'),
browserify = require('browserify'),
factor = require('factor-bundle');
var bundle = browserify({
entries: ['x.js', 'y.js', 'z.js'],
debug: true
});
// Group common dependencies
// -o outputs the entry files without the common dependencies
bundle.plugin('factor-bundle', {
o: ['./static/js/build/x.js',
'./static/js/build/y.js',
'./static/js/build/z.js']
});
// Create Write Stream
var dest = fs.createWriteStream('./static/js/build/common.js');
// Bundle
var stream = bundle.bundle().pipe(dest);
The factor-bundle plugin takes output options o which need to have the same indexes as the entry files.
Unfortunately, I haven't figured out how to do anything else with these files after this point because I can't seem to access factor-bundle's stream event. So for minification etc, it might need to be done also via a browserify plugin.
I have created grunt-reactify to allow you to have a bundle file for a JSX file, in order to make it easier to work with modular React components.
All what you have to do is to specify a parent destination folder and the source files:
grunt.initConfig({
reactify: {
'tmp': 'test/**/*.jsx'
},
})
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('foo') will get exactly the same object returned, if it would resolve to the same file.
Is there a way to invalidate this cache? i.e. for unit testing, I'd like each test to be working on a fresh object.
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();
If you always want to reload your module, you could add this function:
function requireUncached(module) {
delete require.cache[require.resolve(module)];
return require(module);
}
and then use requireUncached('./myModule') instead of require.
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.
"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.
There's a Simple Module for that (with tests)
We had this exact issue while testing our code (delete cached modules so they can be re-required in a fresh state) so we reviewed all the suggestions of people on the various StackOverflow Questions & Answers and put together a simple node.js module (with tests):
https://www.npmjs.com/package/decache
As you would expect, works for both published npm packages and locally defined modules. Windows, Mac, Linux, etc.
How? (usage)
Usage is pretty simple:
install
Install the module from npm:
npm install decache --save-dev
Use it in your code:
// require the decache module:
const decache = require('decache');
// require a module that you wrote"
let mymod = require('./mymodule.js');
// use your module the way you need to:
console.log(mymod.count()); // 0 (the initial state for our counter is zero)
console.log(mymod.incrementRunCount()); // 1
// delete the cached module:
decache('./mymodule.js');
//
mymod = require('./mymodule.js'); // fresh start
console.log(mymod.count()); // 0 (back to initial state ... zero)
If you have any questions or need more examples, please create a GitHub issue:
https://github.com/dwyl/decache/issues
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.
The solutions is to use:
delete require.cache[require.resolve(<path of your script>)]
Find here some basic explanations for those who, like me, are a bit new in this:
Suppose you have a dummy example.js file in the root of your directory:
exports.message = "hi";
exports.say = function () {
console.log(message);
}
Then you require() like this:
$ node
> require('./example.js')
{ message: 'hi', say: [Function] }
If you then add a line like this to example.js:
exports.message = "hi";
exports.say = function () {
console.log(message);
}
exports.farewell = "bye!"; // this line is added later on
And continue in the console, the module is not updated:
> require('./example.js')
{ message: 'hi', say: [Function] }
That's when you can use delete require.cache[require.resolve()] indicated in luff's answer:
> delete require.cache[require.resolve('./example.js')]
true
> require('./example.js')
{ message: 'hi', say: [Function], farewell: 'bye!' }
So the cache is cleaned and the require() captures the content of the file again, loading all the current values.
rewire is great for this use case, you get a new instance with each call. Easy dependency injection for node.js unit testing.
rewire adds a special setter and getter to modules so you can modify their behaviour for better unit testing. You may
inject mocks for other modules or globals like process
leak private variables
override variables within the module.
rewire does not load the file and eval the contents to emulate node's require mechanism. In fact it uses node's own require to load the module. Thus your module behaves exactly the same in your test environment as under regular circumstances (except your modifications).
Good news to all caffeine-addicts: rewire works also with Coffee-Script. Note that in this case CoffeeScript needs to be listed in your devDependencies.
I'd add to luff's answer one more line and change the parameter name:
function requireCached(_module){
var l = module.children.length;
for (var i = 0; i < l; i++)
{
if (module.children[i].id === require.resolve(_module))
{
module.children.splice(i, 1);
break;
}
}
delete require.cache[require.resolve(_module)];
return require(_module)
}
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
I am not 100% certain of what you mean by 'invalidate', but you can add the following above the require statements to clear the cache:
Object.keys(require.cache).forEach(function(key) { delete require.cache[key] })
Taken from #Dancrumb's comment here
requireUncached with relative path: 🔥
const requireUncached = require => module => {
delete require.cache[require.resolve(module)];
return require(module);
};
module.exports = requireUncached;
invoke requireUncached with relative path:
const requireUncached = require('../helpers/require_uncached')(require);
const myModule = requireUncached('./myModule');
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
If you want a module to simply never be cached (sometimes useful for development, but remember to remove it when done!) you can just put delete require.cache[module.id]; inside the module.
here's my version of this answer, which handles not loading a file if it has (for example) syntax errors
function reacquire(module) {
const fullpath = require.resolve(module);
const backup = require.cache[fullpath];
delete require.cache[fullpath];
try {
const newcopy = require(module);
console.log("reqcquired:",module,typeof newcopy);
return newcopy;
} catch (e) {
console.log("Can't reqcquire",module,":",e.message);
require.cache[fullpath] = backup;
return backup;
}
}
Following two step procedure is working perfectly for me.
After changing Model file i-e 'mymodule.js' dynamically, you need to Delete precompiled model in mongoose model first then reload it using require-reload
Example:
// Delete mongoose model
delete mongoose.connection.models[thisObject.singular('mymodule')]
// Reload model
var reload = require('require-reload')(require);
var entityModel = reload('./mymodule.js');
The documentation says:
Modules are cached in this object when they are required. By deleting a key value from this object, the next require will reload the module. This does not apply to native addons, for which reloading will result in an error.
If it's for unit tests, another good tool to use is proxyquire. Everytime you proxyquire the module, it will invalidate the module cache and cache a new one. It also allows you to modify the modules required by the file that you are testing.
I made a small module to delete module from the cache after loading. This forces reevaluation of the module next time it is required. See https://github.com/bahmutov/require-and-forget
// random.js
module.exports = Math.random()
const forget = require('require-and-forget')
const r1 = forget('./random')
const r2 = forget('./random')
// r1 and r2 will be different
// "random.js" will not be stored in the require.cache
PS: you can also put "self-destruct" into the module itself. See https://github.com/bahmutov/unload-me
PSS: more tricks with Node require in my https://glebbahmutov.com/blog/hacking-node-require/