The test runner module mocking options have been consolidated into a single exports property to align with user expectations across different testing tools. While an automated migration script exists, developers should still manually review their mock definitions since code mods can miss edge cases in complex projects. A new command line flag now allows direct control over heap size limits while the crypto module gains support for modern hashing standards like TurboSHAKE and KangarooTwelve. The REPL drops support for the old domain module to keep things lean even if few people used that feature recently.

Node.js 25.9.0 release brings test runner changes and memory controls

The latest Node.js 25.9.0 release includes necessary tweaks to how tests handle module mocking for developers maintaining automated suites. Users who rely on these tools will need to migrate their configuration files before upgrading too soon without checking compatibility first. This version also adds a command line flag for managing heap size limits directly during execution to help with memory leaks.

Node.js 25.9.0 test runner API changes explained

The mock module options have been consolidated into a single exports property that handles both default and named exports now. This change aligns the behavior with what most users expect from other testing frameworks in the ecosystem to reduce confusion across different tools. A codemod tool exists to automate the update but running it blindly on complex projects risks introducing subtle bugs during the transition. Manual review of mock definitions remains the safest path for critical infrastructure code to ensure nothing breaks silently after the switch. The automated migration script is available through npm but should be treated as a starting point rather than a complete fix for every edge case in existing test files.

CLI heap size and crypto algorithm updates

A new --max-heap-size option allows direct control over memory allocation without touching internal configuration files. This feature saves time when debugging out of memory crashes on production servers where config access is restricted for security reasons or operational policies. The crypto module received additions for TurboSHAKE and KangarooTwelve algorithms which support modern hashing standards used in newer protocols. Legacy dependencies within the REPL like node:domain were removed to clean up the codebase even if few people actually used that functionality recently. These changes generally improve performance and stability while keeping the runtime aligned with current web standards without requiring external libraries for basic tasks.

Node.js — Node.js 25.9.0 (Current)

Node.js is a free, open-source, cross-platform JavaScript runtime environment that lets developers create servers, web apps, command line tools and scripts.

Node.js — Node.js 25.9.0 (Current)