I use typescript v5.4.5 (playground) and have an issue. There is my code example

function wrapper<C>(ctx: any, fn: (r: any) => void) {
    const r = {};
    return fn.call(ctx, r);
}

class Example {
    value!: number;

    constructor(v: number) {
        this.value = v;
    }

    getValue() {
        return wrapper(this, function(r) {
            r.value = this.value;
            return r;
        });
    }

    getValueWithArrowFn() {
        return wrapper(this, (r) => {
            r.value = this.value;
            return r;
        });
    }
}

const e = new Example(9999);

console.log(e.getValue());

By logic, this code is fine and can run normally in javascript, because the Function.call allow to call a function with a context, in this example is this, a instance of Example.

The console will log: { value: 9999 }, it works in both javascript and typescript playground. But I don’t know how to let typescript know the type of this in callback of wrapper in getValue method. I have a solution that is to use Arrow Function, but this will make fn.call meaningless.

I try to run this code, it works, but the type inference don’t. I want typescript knows what this in callback (anonymous function) of wrapper in getValue is.

You can see this here:
https://www.typescriptlang.org/play/?#code/GYVwdgxgLglg9mABAdwE4EMAOmCmqA8AwgHwAU0AHgFyLpgCeANIsGDaajXfQJSIC8xRADc4MACZ8A3gChE8xBAQBnKIlQDEUgL4BuOQtQ4oIVElYA6COgA2N8lArNUPfdpkyIN9MuWIAohToALaYNjhaBvLCtiA4AIQ0YCDBAEZ4+lGKKlCoINBwqKTCSSnpLpEKVYhQABYwyhYxNnGawvpV7lkA5sYAarE4pNJZVUYmZigY2HikdQ3MoJCwCBwj1RvqTYOa843NcR2bY8amSKhHG9quWV1VvVADLTgA6jB1AIKoqHDIAGJgYaVTbjM5TLC4Ip7ZhrARCWTHMbbZ67er7QaXRGgyYXUYKa6Y9xdJRgVSICL8RBgHDIAJBULhUgAThZTJunhUcHCFhscG6pBwFgeTziw1cQA