Declaring TypeScript member in prototype rather than adding to 'this'

Question

The following TypeScript:

class A {
    member = "value";
}

...is compiled to:

var A = (function () {
    function A() {
        this.member = "value";
    }
    return A;
})();

I want to achieve the following:

var A = (function () {
    function A() {
    }

    A.prototype.member = "value";

    return A;
})();

The reason for this is that I believe that the latter construct could be more efficient because (1) the assignment this.member = "value" statement would not have to be executed every time a new instance is created, and (2) instance memory payload would be smaller.

Disclaimer: I haven't bench marked the two constructs so I really don't know whether that is the case.

So my question is: Is it possible to declare a "prototype member" using type script?.

I'd also be happy if someone could explain why type script is designed this way?. (See §8.4.1 in the specification)

I understand that it would be stupid to declare mutable members in this way, but declarations of immutable primitives, like string and number, should be fine to set on the prototype, right?

A possible work around could be:

class A {
    member: string;
}

A.prototype.member = "value";

However, that won't work for private members:

class A {
    private member: string;
}

A.prototype.member = "value"; // error TS2107: 'A.member' is inaccessible.

Answer 1

Is it possible to declare a "prototype member" using type script?

No the language doesn't allow this at the moment.

Workaround

When the compiler is unhappy ... assert:

class A {
    private member: string;
}

(<any>A.prototype).member = "value"; // suppressed

why type script is designed this way

Simply because it is non-idiomatic to have non functions on prototype.

(1) the assignment this.member = "value" statement would not have to be executed every time a new instance is created, and (2) instance memory payload would be smaller.

However lookup will definitely be slower. Here is a sample test : http://jsperf.com/prototype-vs-this-access