Is there a way to use typescript or ES7 decorators on members of types?

Question

I'm attempting to set up a simple reflection system using TypeScript or ES7 decorators but am running into an issue in relation to instances wherein only a class is available and not an instance of a class with relation to member decorators. An example of this follows, wherein I would like to be able to access the _foo decorator of DBType without having an instance of the class A available to work with:

console.clear();

function initializeReflection(target) {
    if (target.__reflection) return;
    target.__reflection = {
        classAttributes: [],
        methodAttributes: { },
        propertyAttributes: { },
        accessorAttributes: { }
    }
}

function initializeReflectionMethod(target, name) {
    initializeReflection(target);
    if (target.__reflection)
    if (target.__reflection.methodAttributes[name]) return;
    target.__reflection.methodAttributes[name] = [];
}

function initializeReflectionProperty(target, name) {
    initializeReflection(target);
    if (target.__reflection)
    if (target.__reflection.propertyAttributes[name]) return;
    target.__reflection.propertyAttributes[name] = [];
}

function initializeReflectionAccessor(target, name) {
    initializeReflection(target);
    if (target.__reflection)
    if (target.__reflection.accessorAttributes[name]) return;
    target.__reflection.accessorAttributes[name] = [];
}

function reflectionOf(target) {
    let ret = target;
    if (target.__proto__) ret = target.__proto__;
    return ret.__reflection;
}

function DBType(dbType) {
    if (!(this instanceof DBType)) return function (target, name) {
        initializeReflectionProperty(target, name);
        target.__reflection.propertyAttributes[name].push(new DBType(dbType));
    };
    this._dbType = dbType;
    this.toString = () => {
        return "DBType: " + this._dbType;
    }
}

class A {
    @DBType('VARCHAR(1)')
    _foo = 'a';
}

let a = new A();


console.log('A');
console.log(A, reflectionOf(A));

console.log('a');
console.log(a, reflectionOf(a));

console.log(a.__proto__.__reflection.propertyAttributes._foo[0].toString());

Output:

"A"



class A {
  constructor() {
      _initDefineProp(this, '_foo', _descriptor, this);
  }

}, undefined



"a"



{
  __reflection: {
    accessorAttributes: { ... },
    classAttributes: [],
    methodAttributes: { ... },
    propertyAttributes: { ... }
  },
  _foo: "a"
}, [circular object Object]



"DBType: VARCHAR(1)"

Are decorators even applied to property members prior to instantiation, and if not is there some workaround for this use case which doesn't make the code horribly bloated?