Problem: Track API Usage Metrics Transparently

hard

40 min

Count how many times each service method is called using a Proxy.

Problem statement

Your monitoring system needs to record how frequently different service methods are used, but the service code itself can’t be modified. Adding manual counters inside every method would make the code messy and prone to errors.

Instead, you’ll wrap the service in a Proxy that intercepts all method calls and keeps track of call counts transparently. This tracking layer should be completely invisible to the rest of the application—methods should behave the same, but usage data should accumulate behind the scenes.

Goal

Create a function createTrackedService() that returns a Proxy wrapping a given service object. The Proxy should track the number of times each method is called and expose a .getStats() method to retrieve the metrics.

Constraints

You must use a Proxy with a get trap.
Method behavior must remain unchanged.
Track counts per method name.
Expose a .getStats() method that returns an object like { methodName: callCount }.

Sample output

The examples below illustrate what the output should look like:

Problem: Track API Usage Metrics Transparently

hard

40 min

Count how many times each service method is called using a Proxy.

Problem statement

Goal

Constraints

You must use a Proxy with a get trap.
Method behavior must remain unchanged.
Track counts per method name.
Expose a .getStats() method that returns an object like { methodName: callCount }.

Sample output

The examples below illustrate what the output should look like:

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Log Every Property Read on a Config Object

Prevent Accidental Mutation of Read-Only Settings

Node.js

// Simulated service
class ApiService {
  fetchData() {
    return 'Data fetched';
  }
  postData() {
    return 'Data posted';
  }
}
// Your code here
// Example usage
const service = createTrackedService();
console.log(service.fetchData());
/* Expected output:
Data fetched
*/
console.log(service.postData());
/* Expected output:
Data posted
*/
console.log(service.fetchData());
/* Expected output:
Data fetched
*/
console.log(service.getStats()); // should show call counts per method
/* Expected output:
{ fetchData: 2, postData: 1 }
*/