microsoft / microsoft/TypeScript
`esModuleInterop: true` cause runtime error
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Since Dec 14, 2020.
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Description
Hi there, problems happened when I toggled esModuleInterop flag for my project, I have to because one library it depends enabled this flag.
TypeScript Version: 2.7+
Search Terms:
esModuleInterop
allowSyntheticDefaultImports
Code
import * as apmStar from 'elastic-apm-node'
import SentryDefault from '@sentry/node'
apmStar.start // undefined
SentryDefault // undefined
Explains:
- for
@sentry/nodeit is an es module, soesModuleInterophas no effects on it, but withallowSyntheticDefaultImportsyou can import its default, which property it does not export, so you got an undefined error at runtime - for
elastic-apm-node, it is a commonjs module, and it exports an instance,startis a prototype method of it, so it is lost after__importStar.
But these problems are not informed in the document, guess we could discourage enabling it for library projects?
And I wonder if we could improve type checking for these situations, for example:
- for
apmStar, it is imported as esmodule namespace, so an type error could be thrown when accessing.startmethod on it. - for
SentryDefault, it is a esmodule,allowSyntheticDefaultImportscould be disabled for it
Expected behavior:
Error emitted at compiling time
Actual behavior:
Compiled successfully, but got an error at runtime.
Playground Link:
https://repl.it/@themez1/esModuleInteropTest
Related Issues:
https://github.com/microsoft/TypeScript/issues/28009
https://github.com/microsoft/TypeScript/issues/33954
https://github.com/microsoft/TypeScript/issues/36026
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