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  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

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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   gt  -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

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requireUncached with relative path    const requireUncached   require   gt  module   gt      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

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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    gt  a   a   a from a js   b   b from b js     gt  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    gt  a   a   a from a js   b   b from b js     gt  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

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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  amp  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

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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  gt 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  amp  amp    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

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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

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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

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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

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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

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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

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The solutions is to use   delete require cache require resolve  lt path of your script gt        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  gt  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    gt  require    example js     message   hi   say   Function      That s when you can use delete require cache require resolve    indicated in luff s answer    gt  delete require cache require resolve    example js    true  gt  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

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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

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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

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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

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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

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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  lt  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

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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

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

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