Implicit setters and getters

Hi

This might be more a javascript syntax question, but here goes:

I create a object def like this:

function MyObjectDef()

{

    this.initialize();

};

MyObjectDef.prototype.initialize = function()

{

    this.a = 10;

}

var mo = new MyObjectDef();

alert(mo.a);

Question is, how do I create an implicit setter for that object? I know I could do this:

MyObjectDef.prototype.setA = function(v)

{

    this.a = v*2;

}

mo.setA(10);

alert(mo.a); // would return 20

But I would much prefer something like this (which obviously doesn't work):

MyObjectDef.prototype.set a = function(v)

{

    this.a = v*2;

}

mo.a = 10;

alert(mo.a); // would return 20

Any help?

Thanks,

Jakob