8. Asynchronous Programming

Activity 11: Using Callbacks to Receive Results

Solution:

1. Create a calculate function that takes id and a callback as an argument:

   function calculate(id, callback) {
   }

2. We will first call getUsers to get all of the users. This will give us the address we need:

   function calculate(id, callback) {
   clientApi.getUsers((error, result) => {
   if (error) { return callback(error); }
   const currentUser = result.users.find((user) => user.id === id);
   if (!currentUser) { return callback(new Error('user not found')); }
   });
     }

   Here, we get all of the users, then we apply the find method to the user to find the user we want from the list. If that user does not exist, we call the callback function with the User not found error.

3. Call getUsage to get the user's usage:

   clientApi.getUsage(id, (error, usage) => {
   if (error) { return callback(error); }
     });

   Then, we need to put the call to getUsage inside the callback of...