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On the server, Meteor attempts to avoid bundling node_modules code by replacing entry point modules with a stub that calls module.useNode() (see packages/modules-runtime/server.js). This trick allows evaluating server node_modules natively in Node.js, faithfully preserving all Node-specific behaviors, such as module.id being an absolute file system path, the __dirname and __filename variables, the ability to import binary .node modules, and so on. However, starting in Node.js 12.16.0 (Meteor 1.9.1+), modules evaluated natively by Node are considered ECMAScript modules (ESM) if the closest package.json file has "type": "module" (or has an .mjs file extension). This poses a problem for the module.useNode() trick, because ESM modules cannot be imported synchronously using require (which is currently how module.useNode() works). To work around this new error, this commit checks package.json for "type": "module" in ImportScanner#shouldUseNode to determine whether it's safe to use the module.useNode() trick. The good news is that ESM modules don't have access to nearly as many Node.js-specific quirks: no module, require, or exports variables; no __dirname, no __filename; no ability to import JSON or other non-ESM file types (at least right now). So it seems somewhat less important for ESM code (compared to CommonJS code) to bail out into native Node.js execution using module.useNode(). In other words, bundling server code should not affect its execution in nearly as many cases, if that code is ESM rather than legacy CommonJS. If this good news turns out to be overly optimistic, we can consider using a different kind of bailout stub that's capable of importing ESM using dynamic import(). For now, making sure we avoid bailing out for ESM code like @babel/runtime/helpers/esm/* is the priority.
modules-runtime
Source code of released version | Source code of development version
This package implements the meteorInstall function that is used and
re-exported by the modules package. Do not depend directly on this
package (unless you know what you're doing); depend instead on the
modules package.