const isType = type => target => `[object ${type}]` === Object.prototype.toString.call(target)

const selfIsArray = isType('Array')

Array.selfIsArray || (Object.defineProperty(Array, 'selfIsArray', {
  value: selfIsArray,
  enumerable: false,
  configurable: true,
  writable: true,
}))

console.log(selfIsArray([])) // true