index.js
function defineProperty (obj, name, value) {
  var enumerable = !!obj[name] && obj.propertyIsEnumerable(name)
  Object.defineProperty(obj, name, {
    configurable: true,
    enumerable: enumerable,
    writable: true,
    value: value
  })
}
function defineProperty (obj, name, value) {
  var enumerable = !!obj[name] && obj.propertyIsEnumerable(name)
  Object.defineProperty(obj, name, {
    configurable: true,
    enumerable: enumerable,
    writable: true,
    value: value
  })
}
Sets a property on an object, preserving its enumerability. This function assumes that the property is already writable.