=== /a.js ===
class A { constructor() { this.x = 0; } }
>A : A
>this.x = 0 : 0
>this.x : any
>this : this
>x : any
>0 : 0

/** @implements A*/
class B {}
>B : B

/** @implements A*/
class B2 {
>B2 : B2

    x = 10
>x : number
>10 : 10
}

/** @implements {A}*/
class B3 {
>B3 : B3

    constructor() { this.x = 10 }
>this.x = 10 : 10
>this.x : any
>this : this
>x : any
>10 : 10
}