Don't emit abstract members

[Qwertiy]

TypeScript Version: 3.7 - 4.1.0-dev.20200918

Search Terms:
abstract properties emit useDefineForClassFields

Code

Turn on useDefineForClassFields

abstract class A {
    protected abstract x: number;
}

Expected behavior:

Abstract members are hint for typescript and they don't emit any code. So expected compiled code will be:

"use strict";
class A {
}

Actual behavior:

"use strict";
class A {
    constructor() {
        Object.defineProperty(this, "x", {
            enumerable: true,
            configurable: true,
            writable: true,
            value: void 0
        });
    }
}

Playground Link:
https://www.typescriptlang.org/play?useDefineForClassFields=true&ts=4.1.0-dev.20200918#code/IYIwzgLgTsDGEAJYBthjAgggg3gKAUIQAcoB7CAU3koBMFRIZ4EAPALgQDsBXAWxCUoAbjwBfIA

Consequence of such generation:

There is a larger problem caused by compiling abstract member.

There are 2 ways of override - using property or using getter/setter and they both should be (and are according to ts) compatible with abstract member. But only one of them is fine in runtime.

Code

Turn on useDefineForClassFields

abstract class A {
    protected readonly abstract x: number;

    public doSmth() {
        console.log(this.x)
    }
}

class B extends A {
    protected x = 10
}

class C extends A {
    protected get x() { return 7 }
}

new B().doSmth()
new C().doSmth()

Run compiled code

Expected behavior:

Output:

10 
7

Compiled code:

"use strict";
class A {
    doSmth() {
        console.log(this.x);
    }
}
class B extends A {
    constructor() {
        super(...arguments);
        Object.defineProperty(this, "x", {
            enumerable: true,
            configurable: true,
            writable: true,
            value: 10
        });
    }
}
class C extends A {
    get x() { return 7; }
}
new B().doSmth();
new C().doSmth();

Actual behavior:

Ouptut:

10 
undefined

Compiled code:

"use strict";
class A {
    constructor() {
        Object.defineProperty(this, "x", {
            enumerable: true,
            configurable: true,
            writable: true,
            value: void 0
        });
    }
    doSmth() {
        console.log(this.x);
    }
}
class B extends A {
    constructor() {
        super(...arguments);
        Object.defineProperty(this, "x", {
            enumerable: true,
            configurable: true,
            writable: true,
            value: 10
        });
    }
}
class C extends A {
    get x() { return 7; }
}
new B().doSmth();
new C().doSmth();

Playground Link:
https://www.typescriptlang.org/play?useDefineForClassFields=true&ts=4.1.0-dev.20200918#code/IYIwzgLgTsDGEAJYBthjAgggg3gKAUIQAcoB7CAU3koBMEpLhayA7ZATwVEhngQAeALgSsArgFsQlKAG48BIsTEhkAS1gIWAZQkQAFgAoAlLkVEisNmDLJKAOmRkA5oYNqw9gcfMIAvngBeChoGABCCJQCVKy0GNj4FqQU1FT0AggAvAgAjAAMgQoh6AgAwpHRlLHxZknkVDT0zpSIAia4DC1iUKwIAOz+hXislADuCGEm9jp6Rj4j46VTMwYmQA

Related Issues:
#31225