[BUG] migrate-mongo.cjs is not a proper wrapper for the ESM code

[Simon-Hayden-Dev]

Bug Description

We are using NestJS (which doesn't support ESM) and on app boot run migrate-mongo in-code rather than as a CLI step.

In other words we import * as migrateMongo from 'migrate-mongo'; in our TypeScript code, which gets compiled down to CommonJS require('migrate-mongo'). Hence, at runtime our app will load the migrate-mongo.cjs as defined in the package.json#exports.

However, the code in migrate-mongo.cjs is not the same as migrate-mongo.js. It exposes promises for everything rather than functions. As a result, we get this error:

TypeError: migrateMongo.config.set is not a function

I solved the issue locally by applying a pnpm patch that simply removes the exports from the package.json. That way when we require('migrate-mongo') NodeJS will recognize that it is an ES module and handles the inter-op for us.

---

There is also a second issue with the provided CJS when testing with Jest (and potentially others). Jest doesn't fully support ESM yet. Additionally, Jest uses import/require hooks in order to provide mocked versions of libraries. When you run the dynamic import() inside your .cjs file, Jest will throw an error.

We did fix this by mocking migrate-mongo, such that the actual files aren't even executed at all. But it's not really elegant. And I still need to find a solution for our integration tests.

Environment

• migrate-mongo version: 14.0.7
• Node.js version: 22.22.0
• MongoDB version: Docker 8.2, npm package 6.21.0
• Operating System: Fedora Linux

Steps to Reproduce

1. Create a CommonJS project.
2. Import migrate-mongo
3. Try to use it like you would the ESM version

Expected Behavior

The CJS version should have the same interface as the ESM version.

Actual Behavior

The CJS version exposes Promises for everything, while the ESM version exposes functions.

Error Message

See above.

Additional Context

[maxicapodacqua]

Any updates on this? I'm having the same issue

[Simon-Hayden-Dev]

Any updates on this? I'm having the same issue

Ultimately we used pnpm patch to make migrate-mongo CJS compatible. It's not perfect and definitely breaks in projects that need both ESM and CommonJS to work.

I can paste the file that pnpm put into patches/migrate-mongo.patch and hope it helps. Though you need to properly configure pnpm to apply those patches post-install.

Details

diff --git a/bin/migrate-mongo.js b/bin/migrate-mongo.js
index 462a66b4d5dbecd5ad7bac22d282985801a9de09..57fc1faa5eeb7d0c3f46e73f8b1411e2991d5f5c 100755
--- a/bin/migrate-mongo.js
+++ b/bin/migrate-mongo.js
@@ -5,7 +5,6 @@ import Table from "cli-table3";
 import { createRequire } from 'module';
 import migrateMongo from "../lib/migrate-mongo.js";
 
-const require = createRequire(import.meta.url);
 const pkgjson = require("../package.json");
 
 const program = new Command();
diff --git a/lib/actions/create.js b/lib/actions/create.js
index c033e062000629fba138af5da44b167727cf9894..b4c238819ad21726f0814d5dc39c5d8d28e3d379 100644
--- a/lib/actions/create.js
+++ b/lib/actions/create.js
@@ -5,9 +5,6 @@ import date from "../utils/date.js";
 import migrationsDir from "../env/migrationsDir.js";
 import config from "../env/config.js";
 
-const __filename = fileURLToPath(import.meta.url);
-const __dirname = path.dirname(__filename);
-
 export default async (description) => {
   if (!description) {
     throw new Error("Missing parameter: description");
@@ -22,7 +19,7 @@ export default async (description) => {
     source = await migrationsDir.resolveSampleMigrationPath();
   } else {
     const configContent = await config.read();
-    source = path.join(__dirname, `../../samples/${configContent.moduleSystem}/migration.js`);
+    source = path.join(dirname, `../../samples/${configContent.moduleSystem}/migration.js`);
   }
 
   const filename = `${date.nowAsString()}-${description
diff --git a/lib/actions/init.js b/lib/actions/init.js
index 48fff54941d5180015b96e19ba5d1cc7ff172c86..280f8071b90f6b7fc3c6e4417a95f75ce4b9bca0 100644
--- a/lib/actions/init.js
+++ b/lib/actions/init.js
@@ -2,11 +2,8 @@ import fs from "fs/promises";
 import path from "path";
 import { fileURLToPath } from 'url';
 
-import migrationsDir from "../env/migrationsDir.js";
 import config from "../env/config.js";
-
-const __filename = fileURLToPath(import.meta.url);
-const __dirname = path.dirname(__filename);
+import migrationsDir from "../env/migrationsDir.js";
 
 async function copySampleConfigFile() {
   const moduleSystem = global.options.module === 'esm' ? 'esm' : 'commonjs';
diff --git a/package.json b/package.json
index 53de0d705267e4dae7aa1f3fa98db3caa619442c..fd7a58768135256145424ef1bd1dbb5d47d0d923 100644
--- a/package.json
+++ b/package.json
@@ -4,12 +4,6 @@
   "description": "A database migration tool for MongoDB in Node",
   "type": "module",
   "main": "lib/migrate-mongo.js",
-  "exports": {
-    ".": {
-      "import": "./lib/migrate-mongo.js",
-      "require": "./lib/migrate-mongo.cjs"
-    }
-  },
   "bin": {
     "migrate-mongo": "bin/migrate-mongo.js"
   },
diff --git a/test/actions/create.test.js b/test/actions/create.test.js
index b32d757beb6cd4ccf5c02ed603f12453c41573a7..07e131a3a84256d76cee5bdc8479ebcf1daa234a 100644
--- a/test/actions/create.test.js
+++ b/test/actions/create.test.js
@@ -1,5 +1,4 @@
 import { fileURLToPath } from 'url';
-const __dirname = fileURLToPath(new URL('.', import.meta.url));
 
 import path from "path";
 import fs from "fs/promises";
diff --git a/test/actions/init.test.js b/test/actions/init.test.js
index 3b6a44fbd3e164f0af0fc001c91664463c8eca6e..0dc5bcbd7b875d07f270249f4eb4371bb9f66956 100644
--- a/test/actions/init.test.js
+++ b/test/actions/init.test.js
@@ -1,5 +1,4 @@
 import { fileURLToPath } from 'url';
-const __dirname = fileURLToPath(new URL('.', import.meta.url));
 
 import path from "path";
 import fs from "fs/promises";

For Jest, you still must configure it to transform the .js files to convert them from the ESM syntax to CJS syntax. To do so, add this to your Jest config:

export default {
  // ....
  transformIgnorePatterns: [
    'node_modules/(?!.*\\.mjs$|.*(migrate-mongo)/.*\\.js$)',
  ],
  // ....
}