Create a JavaScript program that checks if a given number is a prime number and handles cases where the input is not a valid integer gracefully, displaying an appropriate error message. The program should take input from the user and display the result.

#include <iostream>
using namespace std;

int main()
{
    int number, i;
    bool isPrime = true;

    cout << "Enter a positive integer: ";
    cin >> number;

    for(i = 2; i <= number / 2; ++i)
    {
        if(number % i == 0)
        {
            isPrime = false;
            break;
        }
    }
    if (isPrime)
        cout << "This is a prime number";
    else
        cout << "This is not a prime number";

    return 0;
}