Testing Node.js 27 early means different rounding in Math and data that older versions can no longer read

The Node.js project on Thursday published an overview on its blog of what the move to the V8 15.6 JavaScript engine means for Node.js 27, whose first alpha appeared at the end of October. Some Math functions may return a different last digit, Math.random produces different sequences for a fixed seed, and large arrays are sorted with a different algorithm. Data stored via structuredClone or v8.serialize gets a new format that older Node.js versions cannot read.

Memory use is changing too: without an explicit setting, the heap may now use up to half of physical memory, capped at 4 GB, and buffer memory counts towards that limit. New features include Math.sumPrecise and Iterator.zip. According to the release notes, Node.js 27 now requires OpenSSL 3 or later, Intel macOS support becomes experimental, and the old domain module is being phased out.

Node.js 27 is the first version under the new schedule of one major release per year, NodeSource explains. A six-month alpha phase is meant for library authors and test pipelines, not production. The first stable version follows in April 2027, and every version will now receive long-term support. Meanwhile, the project has announced security updates for the 22, 24 and 26 lines on 11 November, with the most serious rated high.