Version 21.1.0 (Current)
Notable Changes
Automatically detect and run ESM syntax
The new flag --experimental-detect-module can be used to automatically run ES modules when their syntax can be detected. For “ambiguous” files, which are .js or extensionless files with no package.json with a type field, Node.js will parse the file to detect ES module syntax; if found, it will run the file as an ES module, otherwise it will run the file as a CommonJS module. The same applies to string input via --eval or STDIN.
We hope to make detection enabled by default in a future version of Node.js. Detection increases startup time, so we encourage everyone — especially package authors — to add a type field to package.json, even for the default "type": "commonjs". The presence of a type field, or explicit extensions such as .mjs or .cjs, will opt out of detection.
vm: fix V8 compilation cache support for vm.Script
Previously repeated compilation of the same source code using vm.Script stopped hitting the V8 compilation cache after v16.x when support for importModuleDynamically was added to vm.Script, resulting in a performance regression that blocked users (in particular Jest users) from upgrading from v16.x.
The recent fixes landed in v21.1.0 allow the compilation cache to be hit again for vm.Script when --experimental-vm-modules is not used even in the presence of the importModuleDynamically option, so that users affected by the performance regression can now upgrade. Ongoing work is also being done to enable compilation cache support for vm.CompileFunction.
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