Property 'X' does not exist on type Y

Bug Report

🔎 Search Terms

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about "does not exist on type"

⏯ Playground Link

Playground link with relevant code

💻 Code

type Listener = {
    callback(): boolean;
};

const fn = <T extends Listener>(listener: T) => { };

// this works
fn({
    context: new Map<string, number>(),
    callback() {
        const num = this.context.get('number') ?? 0;

        if (num > 0) return true;
        else return false;
    },
});

// this does not
fn({
    context: new Map<string, number>(),
    callback() {
        const num = this.context.get('number') ?? 0; // Property 'context' does not exist on type 'Listener'.(2339)
        return num > 0;
    },
});

🙁 Actual behavior

It is giving a compilation error as soon as I change the return variable.

🙂 Expected behavior

Should not give compilation errors.

Comienza con el ejemplo enlazado de TypeScript Playground y compara las dos llamadas a fn, centrándote en el tipado contextual y la inferencia genérica para el valor this del callback. El issue estará terminado cuando el segundo ejemplo compile sin el error Property 'context' indicado y conserve el comportamiento del primer ejemplo.