ts assumes a static function in an abstract class needs to be defined

[oakgary]

Bug Report

🔎 Search Terms

This condition will always return true since the function is always defined. Did you mean to call it instead?ts(2774)
static method in abstract class

🕗 Version & Regression Information

This changed between versions 3.8.3 and 4.2.4.
The bug is not fixed in the nightly version.

⏯ Playground Link

Playground link with relevant code

💻 Code

abstract class A {
    static a: () => void;

    public static b(): void {
        if(this.a) {
            console.log('called function b and function a is defined');
        } else {
            console.log('called function b and function a is not defined')
        }
    }
}

class X extends A {

}

class Y extends A {
    static a() {
        //
    }
}

X.b();
Y.b();

🙁 Actual behavior

The error "This condition will always return true since the function is always defined. Did you mean to call it instead?ts(2774)" is displayed on this.a in function b of class A.

🙂 Expected behavior

A static function in an abstract class does not need to be defined. The error should therefore not be displayed.

[RyanCavanaugh]

Duplicate #27899; static members are assumed to have actually been initialized and what you're seeing here is a "missing" error. You should mark this property as optional if it's intentionally sometimes-not-present

[Stirfry70]

[oakgary]

Duplicate #27899; static members are assumed to have actually been initialized and what you're seeing here is a "missing" error. You should mark this property as optional if it's intentionally sometimes-not-present

Actually it is unintentional sometimes-not-present as you cannot make static methods abstract.
The check in function b is there to make sure it is defined.

For anyone stumbling upon this in the future. The error is resolved by marking the function as optional, as suggested by RyanCavanaugh:

abstract class A {
    static a?: () => void;

    public static b(): void {
        if(this.a) {
            console.log('called function b and function a is defined');
        } else {
            console.log('called function b and function a is not defined')
        }
    }
}

class X extends A {

}

class Y extends A {
    static a() {
        //
    }
}

X.b();
Y.b();