ReferenceError with lambda function : "errorMessage": "require is not defined in ES module scope

Question

const AWS = require('aws-sdk');
const s3 = new AWS.S3();

Response
{
  "errorType": "ReferenceError",
  "errorMessage": "require is not defined in ES module scope, you can use import instead",
  "trace": [
    "ReferenceError: require is not defined in ES module scope, you can use import instead",
    "    at file:///var/task/index.mjs:1:13",
    "    at ModuleJob.run (node:internal/modules/esm/module_job:218:25)",
    "    at async ModuleLoader.import (node:internal/modules/esm/loader:329:24)",
    "    at async _tryAwaitImport (file:///var/runtime/index.mjs:1008:16)",
    "    at async _tryRequire (file:///var/runtime/index.mjs:1057:86)",
    "    at async _loadUserApp (file:///var/runtime/index.mjs:1081:16)",
    "    at async UserFunction.js.module.exports.load (file:///var/runtime/index.mjs:1119:21)",
    "    at async start (file:///var/runtime/index.mjs:1282:23)",
    "    at async file:///var/runtime/index.mjs:1288:1"
  ]
}

Answer

Hey Kshitij Kumar,

The issue you're encountering is due to a mismatch between module systems in *JavaScript*, specifically when using *Node.js*. JavaScript has two main types of module systems: **CommonJS (CJS)** and **ECMAScript Modules (ESM)**. Each system has its own syntax for importing and exporting modules:

- **CommonJS** uses `require()` for importing and `module.exports` for exporting. This system is traditionally used in *Node.js* for server-side code.
- **ECMAScript Modules (ESM)** uses `import` and `export` syntax. ESM is a newer standard that's used both in the browser and in *Node.js* for module management.

Your error message `"require is not defined in ES module scope, you can use import instead"` indicates that your code is being treated as an ES module but is attempting to use CommonJS syntax (`require()`) for importing modules. This typically happens in one of the following scenarios:

1. **File Extension**: Your file has a `.mjs` extension, which explicitly marks it as an ES module. Node.js treats `.mjs` files as ES modules by default.

2. **package.json Configuration**: Your `package.json` includes `"type": "module"`, which tells Node.js to treat `.js` files as ES modules within the scope of that package.

In an ES module context, the `require()` function is not defined, as ES modules use the `import` statement for importing modules. This is why the error suggests using `import` instead of `require()`.

To resolve this issue, you need to conform to the ES module syntax for imports:

```javascript
import AWS from 'aws-sdk';
const s3 = new AWS.S3();
```

ReferenceError with lambda function : "errorMessage": "require is not defined in ES module scope

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