feat(ssr): support commonjs in ssrTransform
#3927
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When a dependency is (1) cloned within the Vite root and (2) is listed in `optimizeDeps.exclude`, it will pass through `ssrTransform` and might be using `require` and `module.exports`, so we need to check for that and do some basic replacements. Drawbacks include: - Comments and strings containing `module.exports` or `exports` are not accounted for, so they will be rewritten. Fixes vitejs#2579
aleclarson
commented
Jun 24, 2021
| if (!ssrModule.__esModule) { | ||
| Object.defineProperty(ssrModule, '__esModule', { value: true }) | ||
| if (!Object.getOwnPropertyDescriptor(ssrModule, 'default')) { | ||
| Object.defineProperty(ssrModule, 'default', { value: ssrModule }) |
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This makes a CommonJS module compatible with ESM default import.
ES modules are not affected, since ssrTransform now injects a Object.defineProperty call when ESM syntax is detected.
aleclarson
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Turns out that Closing in favor of a docs PR that mentions this caveat. |
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Description
When a dependency is (1) cloned within the Vite root and (2) is listed in
optimizeDeps.exclude, it will pass throughssrTransformand might be usingrequireandmodule.exports, so we need to check for that and do some basic replacements. Dependencies inssr.noExternalare also affected.Once we know a URL isn't a module (eg: it doesn't use
import,export,import.metaor dynamicimport(...)), we can do the following replacements:requirecalls with__vite_ssr_import__module.exportsandexportsreferences with__vite_ssr_exports__module.exportsassignments with__vite_ssr_exports__.default = xxxThis PR also moves
__esModuledeclaration intossrTransformso CJS modules can be made compatible with ESM import by automatically assigningexports.default = exportswithinssrModuleLoaderif it's undefined. This allowsimport foo from 'cjs'to work as expected.Additional context
Fixes #2579
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fixes #123).