Consider the following code:

type TParser = (str: string, errStr: string) => number;

function LIT(str: string): TParser {
    return function (input: string, errStr="An error occurred"): number {
        if (input.startsWith(str)) {
            return str.length;
        } else {
            console.log(errStr);
            return -1;
        }
    }
}

let func = LIT("abc");
let result = func("abc");

The function returned from LIT('abc') is a function that should take either 1 or 2 arguments because a default value was provided for the second parameter. However, when I run this script, I get this error:

TS2554 [ERROR]: Expected 2 arguments, but got 1.
let result = func('abc')
             ~~~~
    at file:///C:/Users/johnd/hera/source/bug.ts:17:14

    An argument for 'errStr' was not provided.
    type TParser = (str: string, errStr: string) => number;
                                 ~~~~~~~~~~~~~~
        at file:///C:/Users/johnd/hera/source/bug.ts:1:30

error: Type checking failed.

Am I doing something wrong or is this a TypeScript bug? In my opinion, if I'm not allowed to provide default values for a function returned from another function, TypeScript should at least warn me that it's invalid TypeScript.

In case it's relevant, I'm using Deno (not Node.js). Here is version info, though I believe that deno just defers to TypeScript, so it's the TypeScript version that's relevant:

$ deno --version
deno 2.5.6 (stable, release, x86_64-pc-windows-msvc)
v8 14.0.365.5-rusty
typescript 5.9.2