No error report on duplicated function/class declaration

[xryeisme]

Bug Report

🔎 Search Terms

🕗 Version & Regression Information

⏯ Playground Link

https://www.typescriptlang.org/play

💻 Code

declare function foo() : any

declare class foo {
    test() : any
}

🙁 Actual behavior

no error report

🙂 Expected behavior

I think it should report error because we have duplicated 'foo' defintion.

[fatcerberus]

https://www.typescriptlang.org/docs/handbook/declaration-merging.html

“it’s a feature, not a bug” 😉

[RyanCavanaugh]

This is the syntax you would use to describe an object which is callable both with and without new, which is a thing that people do in JS sometimes.

[MartinJohns]

which is a thing that people do in JS sometimes.

@RyanCavanaugh Your comment is roughly 2 weeks to early.

[xryeisme]

this is confused, because it report errors if without 'declare' keyword:

function foo() : any {}

// Class declaration cannot implement overload list for 'foo'.(2813)
class foo {
  test() : any {}
}

so can I just simpliy assume that the declaration with 'declare' is like something in header file for js but not for ts?

[MartinJohns]

the declaration with 'declare' is like something in header file for js but not for ts?

Yes. It basically tells TypeScript that this will exist at runtime.

[xryeisme]

clear now, close this issue, thanks everyone for clarification