promise.js
function defineConfigurable ( obj, key, val ) {
    Object.defineProperty(obj, key, {
      configurable: true,
      enumerable: false,
      writable: true,
      value: val
    });
  }
function defineConfigurable ( obj, key, val ) {
    Object.defineProperty(obj, key, {
      configurable: true,
      enumerable: false,
      writable: true,
      value: val
    });
  }
set a value as configurable and non-enumerable