var a = "1",
        b = "hello",
        c = { "100" : "some important data" },
        d = {};

        d[a]["greeting"] = b;
        d[a]["data"] = c;

        console.debug (d);

d[a] = {
    greetings: b,
    data: c
};

d = new function () {
    this[a] = {
        greetings: b,
        data: c
    };
};

d = {
  [a]: {
    greetings: b,
    data: c
  }
};

d[a] = [];
d[a]["greeting"] = b;

console.debug(d);