fix(#78): move instance from module to global scope

Author: skonves

index.js

@@ -1,10 +1,16 @@
 'use strict';
 
 const { AsyncLocalStorage } = require('async_hooks');
-const asyncLocalStorage = new AsyncLocalStorage();
+
+const STORAGE_KEY = Symbol.for(
+	'skonves/express-http-context/asyncLocalStorage',
+);
+
+globalThis[STORAGE_KEY] = globalThis[STORAGE_KEY] ?? new AsyncLocalStorage();
 
 /** Express.js middleware that is responsible for initializing the context for each request. */
 function middleware(req, res, next) {
+  const asyncLocalStorage = globalThis[STORAGE_KEY];
   if (!asyncLocalStorage.getStore()) {
     asyncLocalStorage.run(new Map(), () => next());
   } else {
@@ -17,7 +23,7 @@ function middleware(req, res, next) {
  * @param {string} key
  */
 function get(key) {
-	return asyncLocalStorage.getStore()?.get(key);
+	return globalThis[STORAGE_KEY].getStore()?.get(key);
 }
 
 /**
@@ -26,6 +32,7 @@ function get(key) {
  * @param {*} value
  */
 function set(key, value) {
+  const asyncLocalStorage = globalThis[STORAGE_KEY];
 	if (asyncLocalStorage.getStore()) {
 		asyncLocalStorage.getStore()?.set(key, value);
 		return value;
@@ -37,5 +44,5 @@ module.exports = {
 	middleware,
 	get: get,
 	set: set,
-	asyncLocalStorage
+	asyncLocalStorage: globalThis[STORAGE_KEY],
 };

tests/express-test-harness.js

@@ -260,20 +260,9 @@ describe('express-http-context', function () {
 		expect(response1.header[REQUEST_ID_IN_RESPONSE_HTTP_HEADER_NAME]?.length).toBe(21);
 		expect(response2.header[REQUEST_ID_IN_RESPONSE_HTTP_HEADER_NAME]?.length).toBe(21);
 
-		// This is the specific example I had flagged in the Github issue (#26, #78) - where
-		// setting something into the httpContext in a common library, but it's
-		// unusable from within the application code.
 		expect(response1.body.requestId).toBe(response1.header[REQUEST_ID_IN_RESPONSE_HTTP_HEADER_NAME]);
 		expect(response2.body.requestId).toBe(response2.header[REQUEST_ID_IN_RESPONSE_HTTP_HEADER_NAME]);
 
-		// These operations also fail, I suspect, because neither of the set/get
-		// functions are usable, because the directly imported AsyncLocalStorage has
-		// not been initialised by a call to `app.use(middleware)` within our code
-		// here.  Effectively this is another manifestation of the same bug -
-		// showing that although the middleware *has* already been initialised in
-		// Express request handler chain, it is not usable because the
-		// AsyncLocalStorage context is not identical for all usages of the
-		// `express-http-context` library code.
 		expect(response1.body.valueFromContext).toBe('value1');
 		expect(response2.body.valueFromContext).toBe('value2');
 	});