Using ES Module packages in Azure Typescript Function

Question

I am unable to use the package p-map in my Azure Function. I get the following error:

Worker failed to load function: 'serverless' with function id: '<id>'.
Result: Failure
Exception: Worker was unable to load function serverless: 'Error [ERR_REQUIRE_ESM]: require() of ES Module <es-module> from /usr/local/Cellar/azure-functions-core-tools@4/4.0.4483/workers/node/worker-bundle.js not supported.
Instead change the require of index.js in /usr/local/Cellar/azure-functions-core-tools@4/4.0.4483/workers/node/worker-bundle.js to a dynamic import() which is available in all CommonJS modules.'

The project is created by following the steps in Azure's documentation . The following is in the index.ts:

import { AzureFunction, Context, HttpRequest } from "@azure/functions";
import pMap from "p-map";
import got from "got";

const httpTrigger: AzureFunction = async function (context: Context, req: HttpRequest): Promise<void> {
    const sites = [
        'https://avajs.dev',
        'https://github.com'
    ];

    const mapper = async site => {
        const {requestUrl} = await got.head(site);
        return requestUrl;
    };

    const result = await pMap(sites, mapper, {concurrency: 2});
    

    context.res = {
        // status: 200, /* Defaults to 200 */
        body: result
    };

};

export default httpTrigger;

My tsconfig.json looks like following:

{
  "compilerOptions": {
    "module": "es2020",
    "target": "es2020",
    "outDir": "dist",
    "rootDir": ".",
    "sourceMap": true,
    "strict": false,
    "moduleResolution": "node",
    "allowSyntheticDefaultImports": true
  }
}

Lastly, this is my package.json:

{
  "name": "azure-functions-test",
  "version": "1.0.0",
  "description": "",
  "type": "module",
  "scripts": {
    "build": "tsc",
    "watch": "tsc -w",
    "prestart": "npm run build",
    "start": "func start",
    "test": "echo \"No tests yet...\""
  },
  "dependencies": {
    "got": "^12.0.4",
    "p-map": "^5.3.0"
  },
  "devDependencies": {
    "@azure/functions": "^3.0.0",
    "typescript": "^4.0.0"
  }
}

p-map is strictly an ES Module and cannot be used in CommonJS projects.

Am I missing something or is it just not possible to use ES Module packages in Azure Functions? Thanks in advance.

GitHub repository of aforementioned code to test things out locally: azure-functions-test

Answer 1

I resolved my issue by renaming my index.ts file to index.mts. This built a index.mjs file (after running npm run build ) in my dist folder which fixed the issue.

One thing to note is that you also have to edit your function.json's scriptFile key so it uses your.mjs file instead of non-existing.js file.

Answer 2

According to the docs on Node.js' website, specifying "type": "module" in your package.json should also indicate if Node should use ESM.

Here's what I did to get ESM working for my functions in my Function App:

tsconfig.json

{
  "compilerOptions": {
    "module": "ESNext",
    "target": "ESNext",
    "moduleResolution": "Node",
    "outDir": "dist",
    "rootDir": ".",
    "sourceMap": true,
    "strict": false,
    "noImplicitAny": true,
    "noUnusedLocals": true
  }
}

Some relevant function app settings:

WEBSITE_NODE_DEFAULT_VERSION : ~16 (To run using Node.js 16 runtime) FUNCTIONS_EXTENSION_VERSION : ~4