javascript设置样式属性覆盖

Question

(function (constructor) {
  if (constructor && constructor.prototype) {

    //Custom - styleMe
    Object.defineProperty(constructor.prototype, 'styleMe', {
      get: function () {
        if (this == null) return {};
        return (window.getComputedStyle ? getComputedStyle(this, null) : this.currentStyle);
      },
      set: function (key, newValue) {
        this.styleMe.key = newValue;
      }
    });
  }
})(window.Node || window.Element);

我可以轻松get样式值，如：

var marginTop = document.getElementById("myID").styleMe.marginTop;

但是，如何设定价值？这不起作用：

document.getElementById("myID").styleMe.marginTop = "30px";