var sameArray = [1, 2, 3, 4];

var diffArray = ['a', 'b', 'c', 4];

​

//3rd party function implementation

function getItemsType(arr) {

  var itemType, i;

  for (i=0; i < arr.length; i++) {

    if (typeof itemType === 'undefined') {

      itemType = typeof arr[i];

    } else if (itemType !== typeof arr[i]) {

      return undefined;

    }

  }

  return itemType;

}

​

console.log(getItemsType(sameArray));

console.log(getItemsType(diffArray));

​

​

//Array prototype integration

Array.prototype.itemPrototype = function () {

  var itemType, i;

  for (i=0; i < this.length; i++) {

    if (typeof itemType === 'undefined') {

      itemType = typeof this[i];

    } else if (itemType !== typeof this[i]) {

      return undefined;

    }

  }

  return itemType;

};

​

console.log(sameArray.itemPrototype());

console.log(diffArray.itemPrototype());