`esModuleInterop: true` cause runtime error

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@rbuckton 已经在做这个了。

开始于 2020年12月14日。

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描述

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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/node it is an es module, so esModuleInterop has no effects on it, but with allowSyntheticDefaultImports you 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, start is 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 .start method on it.
  • for SentryDefault, it is a esmodule, allowSyntheticDefaultImports could 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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