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38. functions / edge-middleware: edge runtime

Last updated on Aug 05, 2025

Understanding Edge Runtime: A Comprehensive Guide

Edge runtime is a powerful tool that extends JavaScript capabilities, enabling developers to create more efficient and scalable applications. This guide provides an in-depth look at the features, limitations, and best practices of working with Edge runtime.

Introduction to Edge Runtime

Edge runtime is a JavaScript execution environment designed for high-performance tasks such as data processing, machine learning inference, and real-time analytics. It leverages advanced optimizations like Just-In-Time (JIT) compilation and memory management techniques to deliver superior performance compared to traditional interpreters.

Checking the Edge Runtime

To determine if your function is executing within the Edge runtime, you can utilize the globalThis.EdgeRuntime property. This check is particularly useful for validation in testing environments or when requiring different APIs based on the runtime context.

if (typeof globalThis.EdgeRuntime !== 'string') {
  // Code executed only in Edge runtime
}

Supported APIs

Edge runtime supports a wide range of JavaScript and Node.js APIs, ensuring compatibility with existing development workflows.

Network APIs

  • DNS resolution
  • HTTP/HTTPS requests
  • WebSocket connections

Encoding APIs

  • Base64 encoding/decoding
  • URL encoding/decoding

Stream APIs

  • Readable and Writable streams
  • File system operations

Crypto APIs

  • AES encryption
  • HMAC signature generation

Other Web Standard APIs

  • JSON manipulation
  • Date/time functions
  • Regular expressions

Compatible Node.js Modules

Edge runtime supports several Node.js modules, enhancing functionality while maintaining compatibility.

Module Name | Description

--- | --- async_hooks | Manages async resources with AsyncLocalStorage. events | Facilitates event-driven programming. buffer | Efficient memory management for binary data.

Unsupported APIs

While Edge runtime offers extensive support, some Node.js APIs are restricted to ensure compatibility and security.

Restricted Features

  • File system operations beyond supported methods
  • Use of require for native modules; prefer import
  • Dynamic WebAssembly compilation from buffers

Environment Variables

Access environment variables using process.env, enabling configuration flexibility for various deployment scenarios.

Example Usage

const port = process.env.PORT || 8080;

Conclusion

Edge runtime provides a robust environment for JavaScript developers, balancing performance and flexibility. By leveraging supported APIs and modules while adhering to limitations, developers can optimize their applications for high-performance tasks. Regular checks on the runtime environment ensure compatibility and proper resource management.