Node v22.10.0 (Current)
This release introduces a "module-sync" exports condition that's enabled when require(esm) is enabled, so packages can supply a synchronous ES module to the Node.js module loader, no matter if it's being required or imported. This is similar to the "module" condition that bundlers have been using to support require(esm) in Node.js, and allows dual-package authors to opt into ESM-first only on newer versions of Node.js that supports require(esm) to avoid the dual-package hazard.
Or if the package is only meant to be run on Node.js and wants to fallback to CJS on older versions that don't have require(esm):
For package authors: this only serves as a feature-detection mechanism for packages that wish to support both CJS and ESM users during the period when some active Node.js LTS versions support require(esm) while some older ones don't. When all active Node.js LTS lines support require(esm), packages can simplify their distributions by bumping the major version, dropping their CJS exports, and removing the module-sync exports condition (with only main or default targetting the ESM exports). If the package needs to support both bundlers and being run unbundled on Node.js during the transition period, use both module-sync and module and point them to the same ESM file. If the package already doesn't want to support older versions of Node.js that doesn't support require(esm), don't use this export condition.
For bundlers/tools: they should avoid implementing this stop-gap condition. Most existing bundlers implement the de-facto bundler standard module exports condition, and that should be enough to support users who want to bundle ESM from CJS consumers. Users who want both bundlers and Node.js to recognize the ESM exports can use both module/module-sync conditions during the transition period, and can drop module-sync+module when they no longer need to support older versions of Node.js. If tools do want to support this condition, it's recommended to make the resolution rules in the graph pointed by this condition match the Node.js native ESM rules to avoid divergence.
