Ptototype Inheritance just is not the same for Class instances not

ClassInstancePrototypeChainTest.js

class A {
    a = 1
    constructor() {
        console.log('A constructor this.a : ', this.a);
        this.a = 1;
        console.log('A constructor this.a : ', this.a);
    }
}

class B extends A {
    a = 2
    constructor() {
        super();
        console.log('B constructor this.a : ', this.a);
        this.a = 2;
        console.log('B constructor this.a : ', this.a);
    }
}

class C extends B {
    a = 3
    constructor() {
        super();
        console.log('C constructor this.a : ', this.a);
        this.a = 3;
        console.log('C constructor this.a : ', this.a);
    }
}

console.log('\n\n so here we go with construction : \n');

const instanceC = new C;

console.log('\n\n and now we are checking instance : \n');

console.log('instanceC.a      : ', instanceC.a);                               // 3, exactly as expected
const instanceProtoB = Object.getPrototypeOf(instanceC);
console.log('instanceProtoB.a : ', instanceProtoB.a);                 // undefined, should be 2
const instanceProtoA = Object.getPrototypeOf(instanceProtoB);
console.log('instanceProtoA.a : ', instanceProtoA.a);                 // undefined, should be 1

console.log('\n\n then here are instanceof checks : \n');

console.log('instanceC instanceof A : ', instanceC instanceof A);
console.log('instanceC instanceof B : ', instanceC instanceof B);
console.log('instanceC instanceof C : ', instanceC instanceof C);
console.log('\n');

console.log('instanceC_ProtoB instanceof A : ', instanceProtoB instanceof A);
console.log('instanceC_ProtoB instanceof B : ', instanceProtoB instanceof B);
console.log('instanceC_ProtoB instanceof C : ', instanceProtoB instanceof C);
console.log('\n');

console.log('instanceC_ProtoA instanceof A : ', instanceProtoA instanceof A);
console.log('instanceC_ProtoA instanceof B : ', instanceProtoA instanceof B);
console.log('instanceC_ProtoA instanceof C : ', instanceProtoA instanceof C);

console.log('\n');