We review a coding question to determine the count of numbers that have 4 as a digit from 1 to n.

int getCount(int n)
{
  int count = 0;
  for (int i = 0; i < n; i++)
           if (has4(i)) count ++;
  return count;
}

bool has4(int n)
{
   while (x != 0)
   {
        if (x%10 == 4)
          return true;
        x = x / 10;
   }
   return false;
}

We review webhooks today. We discussed that they were useful for notifications in REST API implementation.

In addition, Web hooks do the following :
1) keep Data in sync
2) give other applications a chance to do something
3) provide necessary params on certain events

Web hooks take a URL to send the notification to. A "postbin" web service will receive and log the notifications so that it can monitor all POST HTTP requests it receives.  This URL is taken from a registration form hosted by the publisher.  When this notification arrives, the subscriber can choose to respond by making additional API calls based on the information in the notification.

If the registration is to be avoided, APIs can optionally take a callback parameter that takes in a URI. This way during the execution of this specific API, a POST method will be called on the URI provided with a predetermined template of information. This lets the caller subscribe and unsubscribe dynamically.