如何在 node.js 中的“require”之后删除模块？

Question

Let say, after I require a module and do something as below:

var b = require('./b.js');
--- do something with b ---

Then I want to take away module b (ie clean up the cache). how I can do it?

The reason is that I want to dynamically load/ remove or update the module without restarting node server. any idea?

------- more -------- based on the suggestion to delete require.cache, it still doesn't work...

what I did are few things:
1) delete require.cache[require.resolve('./b.js')];
2) loop for every require.cache's children and remove any child who is b.js
3) delete b

However, when i call b, it is still there! it is still accessible. unless I do that:

b = {};

not sure if it is a good way to handle that. because if later, I require ('./b.js') again while b.js has been modified. Will it require the old cached b.js (which I tried to delete), or the new one?

----------- More finding --------------

ok. i do more testing and playing around with the code.. here is what I found:

1) delete require.cache[]  is essential.  Only if it is deleted, 
 then the next time I load a new b.js will take effect.
2) looping through require.cache[] and delete any entry in the 
 children with the full filename of b.js doesn't take any effect.  i.e.
u can delete or leave it.  However, I'm unsure if there is any side
effect.  I think it is a good idea to keep it clean and delete it if
there is no performance impact.
3) of course, assign b={} doesn't really necessary, but i think it is 
 useful to also keep it clean.

Answer 1

You can use this to delete its entry in the cache:

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

require.resolve() will figure out the full path of ./b.js , which is used as a cache key.

Answer 2

One of the easiest ways (although not the best in terms of performance as even unrelated module's caches get cleared) would be to simply purge every module in the cache

Note that clearing the cache for *.node files (native modules) might cause undefined behaviour and therefore is not supported ( https://github.com/nodejs/node/commit/5c14d695d2c1f924cf06af6ae896027569993a5c ), so there needs to be an if statement to ensure those don't get removed from the cache, too.

    for (const path in require.cache) {
      if (path.endsWith('.js')) { // only clear *.js, not *.node
        delete require.cache[path]
      }
    }

Answer 3

Spent some time trying to clear cache in Jest tests for Vuex store with no luck. Seems like Jest has its own mechanism that doesn't need manual call to delete require.cache.

beforeEach(() => {
  jest.resetModules();
});

And tests:

let store;

it("1", () => {
   process.env.something = true;
   store = require("@/src/store.index");
});

it("2", () => {
   process.env.something = false;
   store = require("@/src/store.index");
});

Both stores will be different modules.

Answer 4

I have found the easiest way to handle invalidating the cache is actually to reset the exposed cache object. When deleting individual entries from the cache, the child dependencies become a bit troublesome to iterate through.

 require.cache = {};

Answer 5

I found this useful for client side applications. I wanted to import code as I needed it and then garbage collect it when I was done. This seems to work. I'm not sure about the cache, but it should get garbage collected once there is no more reference to module and CONTAINER.sayHello has been deleted.

/* my-module.js */

function sayHello { console.log("hello"); }

export { sayHello };

/* somewhere-else.js */

const CONTAINER = {};

import("my-module.js").then(module => {

  CONTAINER.sayHello = module.sayHello;

  CONTAINER.sayHello(); // hello

  delete CONTAINER.sayHello;

  console.log(CONTAINER.sayHello); // undefined

});