Type of this is not preserved when class method is used as a value

[zawodskoj]

Bug Report

🔎 Search Terms

this type, class, bind

⏯ Playground Link

Playground link with relevant code

💻 Code

class Foo {
    bar = 123;

    method() {
        console.log(this.bar);
    }
}

const instance = new Foo();
const fn1 = instance.method;
fn1(); // compiles, but fails in runtime

const fn2: (this: Foo) => void = instance.method;
fn2(); // does not compile: The 'this' context of type 'void' is not assignable to method's 'this' of type 'Foo'.

// TS allows to coerce `this` in any (and unsafe) way
const fn3: (this: number) => void = instance.method;
fn3.bind(123)(); // compiles, but fails in runtime

🙁 Actual behavior

TS assumes this as any

🙂 Expected behavior

TS should preserve this type when class method is used as a value

[fatcerberus]

Methods don’t have a this type by default. See #10288 and #7968

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.