why Map<string,boolean> reuturn type boolean | undefined

[HomyeeKing]

Bug Report

🔎 Search Terms

🕗 Version & Regression Information

• This is a crash

⏯ Playground Link

Playground link with relevant code

💻 Code

function test(id:string,map:Map<string,boolean>):boolean{
    if(map.has(id)){
        return map.get(id)  // why the type here is boolean | undefined? 
    }
}

🙁 Actual behavior

Type 'boolean | undefined' is not assignable to type 'boolean'.

🙂 Expected behavior

because I've set the type is Map<string,boolean>, so it is boolean, no way undefined

[nmain]

Duplicate of #13086
Search terms: map has narrowing

[HomyeeKing]

so in this case , we've done type guard by if condition, so it does exist and won't be deleted in common use case

[nmain]

I agree, the code is sound, but tsc has no way to make this kind of reasoning.

[typescript-bot]

This issue has been marked as 'Question' and has seen no recent activity. It has been automatically closed for house-keeping purposes. If you're still waiting on a response, questions are usually better suited to stackoverflow.