About the typeof ES6 import expression

[suguanYang]

🔎 Search Terms

typeof import("x") should be the same as the return type of import expression call

🕗 Version & Regression Information

All version

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/JYWwDg9gTgLgBAKjgQwM5wEoFNkGN4BmUEIcA5FDvmQNwBQuEAdqvJXvALxyiSwAUFKjDIBKenRgBPMFjgBJVAFEAjgFdkAGwA8AFQA0cAKoA+ON11wsADxhYmAE3RG4AfmNXb9p3EvuYUGpyAFxwBFqoIWERWBKSMnKKqhqa2KhqmjAAjOYKyupa2tKyEARw7PiGxVilPODQMIIVIqImNHAA9B3RmpHxsnnJWmkZMABMuUkFOtW12BxVCbW8DU3CYm2d3QFBdHRAA

💻 Code

import * as React from 'react';
const react = import('react');

type IsEqual<T, U> = T extends U ? U extends T ? true : false : false;

🙁 Actual behavior

type IsEqualResult1 = IsEqual<typeof react, typeof import('react')>; // false
type IsEqualResult2 = IsEqual<typeof React, typeof import('react')>; // true

🙂 Expected behavior

type IsEqualResult1 = IsEqual<typeof react, typeof import('react')>; // true
type IsEqualResult2 = IsEqual<typeof React, typeof import('react')>; // false

Additional information about the issue

No response

[MartinJohns]

import() has different semantics/types at type and value level. At value level the import() call returns a Promise<>.

[kirkwaiblinger]

Even after awaiting, there's also differences regarding default vs namespace imports due to TS's ES Module interop... we can get the line to be true like so

[suguanYang]

import() has different semantics/types at type and value level. At value level the import() call returns a Promise<>.

I'm trying to make this more clear to me:
The typeof import() expression call is just another form of typeof namespace in types annotation, if a module itself has namespace, it will make the value of import and the type of import at different level.

Is this right?

[typescript-bot]

This issue has been marked as "Not a Defect" and has seen no recent activity. It has been automatically closed for house-keeping purposes.