AWS Compute Blog

Node.js 18.x runtime now available in AWS Lambda

This post is written by Suraj Tripathi, Cloud Consultant, AppDev.

You can now develop AWS Lambda functions using the Node.js 18 runtime. This version is in active LTS status and considered ready for general use. When creating or updating functions, specify a runtime parameter value of nodejs18.x or use the appropriate container base image to use this new runtime.

This runtime version is supported by functions running on either Arm-based AWS Graviton2 processors or x86-based processors. Using the Graviton2 processor architecture option allows you to get up to 34% better price performance.

This blog post explains the major changes available with the Node.js 18 runtime in Lambda.

AWS SDK for JavaScript upgrade to v3

Lambda’s Node.js runtimes include the AWS SDK for JavaScript. This enables customers to use the AWS SDK to connect to other AWS services from their function code, without having to include the AWS SDK in their function deployment. This is especially useful when creating functions in the AWS Management Console. It’s also useful for Lambda functions deployed as inline code in CloudFormation templates.

Up until Node.js 16, Lambda’s Node.js runtimes have included the AWS SDK for JavaScript version 2. This has since been superseded by the AWS SDK for JavaScript version 3, which was released in December 2020. With this release, Lambda has upgraded the version of the AWS SDK for JavaScript included with the runtime from v2 to v3.

If your existing Lambda functions are using the included SDK v2, then you must update your function code to use the SDK v3 when upgrading to the Node.js 18 runtime. This is the recommended approach when upgrading existing functions to Node.js 18. Alternatively, you can use the Node.js 18 runtime without updating your existing code if you deploy the SDK v2 together with your function code.

Version 3 of the SDK for JavaScript offers many benefits over version 2. Most importantly, it is modular, so your code only loads the modules it needs. Modularity also reduces your function size if you choose to deploy the SDK with your function code rather than using the version built into the Lambda runtime. Learn more about optimizing Node.js dependencies in Lambda here.

For example, for a function interacting with Amazon S3 using the v2 SDK, you import the entire SDK, even though you don’t use most of it:

const AWS = require("aws-sdk");

With the v3 SDK, you only import the modules you need, such as ListBucketsCommand, and a service client like S3Client.

import { S3Client, ListBucketsCommand } from "@aws-sdk/client-s3";

Another difference between SDK v2 and SDK v3 is the default settings for TCP connection re-use. In the SDK v2, connection re-use is disabled by default. In SDK v3, it is enabled by default. In most cases, enabling connection re-use improves function performance. To stop TCP connection reuse, set the AWS_NODEJS_CONNECTION_REUSE_ENABLED environment variable to false. You can also stop keeping the connections alive on a per-service client basis.

For more information, see Why and how you should use AWS SDK for JavaScript (v3) on Node.js 18.

Support for ES module resolution using NODE_PATH

Another change in the Node.js 18 runtime is added support for ES module resolution via the NODE_PATH environment variable.

ES modules are supported by Lambda’s Node.js 14 and Node.js 16 runtimes. They enable top-level await, which can lower cold start latency when used with Provisioned Concurrency. However, by default Node.js does not search the folders in the NODE_PATH environment variable when importing ES modules. This makes it difficult to import ES modules from folders outside of the /var/task/ folder in which the function code is deployed. For example, to load the AWS SDK included in the runtime as an ES module, or to load ES modules from Lambda layers.

The Node.js 18.x runtime for Lambda searches the folders listed in NODE_PATH when loading ES modules. This makes it easier to include the AWS SDK as an ES module or load ES modules from Lambda layers.

Node.js 18 language updates

The Lambda Node.js 18 runtime also enables you to take advantage of new Node.js 18 language features. This includes improved performance for class fields and private class methods, JSON import assertions, and experimental features such as the Fetch API, Test Runner module, and Web Streams API.

JSON import assertion

The import assertions feature allows module import statements to include additional information alongside the module specifier. Now the following code is valid:

// index.mjs

// static import
import fooData from './foo.json' assert { type: 'json' };

// dynamic import
const { default: barData } = await import('./bar.json', { assert: { type: 'json' } });

export const handler = async(event) => {

    // logs data in foo.json file
    // logs data in bar.json file

    const response = {
        statusCode: 200,
        body: JSON.stringify('Hello from Lambda!'),
    return response;


  "foo1" : "1234",
  "foo2" : "4678"


  "bar1" : "0001",
  "bar2" : "0002"

Experimental features

While still experimental, the global fetch API is available by default in Node.js 18. The API includes a fetch function, making fetch polyfills and third-party HTTP packages redundant.

// index.mjs 

export const handler = async(event) => {
    const res = await fetch('');
    if (res.ok) {
      const data = await res.json();

    const response = {
        statusCode: 200,
        body: JSON.stringify('Hello from Lambda!'),
    return response;

Experimental features in Node.js can be enabled/disabled via the NODE_OPTIONS environment variable. For example, to stop the experimental fetch API you can create a Lambda environment variable NODE_OPTIONS and set the value to --no-experimental-fetch.

With this change, if you run the previous code for the fetch API in your Lambda function, it throws a reference error because the experimental fetch API is now disabled.


Node.js 18 is now supported by Lambda. When building your Lambda functions using the zip archive packaging style, use a runtime parameter value of nodejs18.x to get started building with Node.js 18.

You can also build Lambda functions in Node.js 18 by deploying your function code as a container image using the Node.js 18 AWS base image for Lambda. You may learn more about writing functions in Node.js 18 by reading about the Node.js programming model in the Lambda documentation.

For existing Node.js functions, review your code for compatibility with Node.js 18, including deprecations, then migrate to the new runtime by changing the function’s runtime configuration to nodejs18.x.

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