Problem: Track Function Call Count with a Decorator

Medium

30 min

Wrap a function with a decorator that counts and logs how many times it’s been called.

Problem statement

You’re debugging a utility function that’s being overused in production. You want to track how many times it’s called—without modifying the function itself. We’ll use a decorator to wrap it, maintain an internal counter, and log the count of each invocation. This is a common real-world pattern when adding metrics, telemetry, or usage tracking to shared utilities.

Goal

Create a withCallCount decorator that:

Tracks how many times the wrapped function has been called.
Logs [COUNT] Function <name> called N times.
Works with both synchronous and asynchronous functions.
Preserves the original return value.

Constraints

Do not modify the original function.
Do not use global variables.
The decorator must maintain state internally (use closures).
Preserve the original function’s name in logs.

Sample output

The examples below illustrate what the output should look like:

Problem: Track Function Call Count with a Decorator

Medium

30 min

Wrap a function with a decorator that counts and logs how many times it’s been called.

Problem statement

Goal

Create a withCallCount decorator that:

Tracks how many times the wrapped function has been called.
Logs [COUNT] Function <name> called N times.
Works with both synchronous and asynchronous functions.
Preserves the original return value.

Constraints

Do not modify the original function.
Do not use global variables.
The decorator must maintain state internally (use closures).
Preserve the original function’s name in logs.

Sample output

The examples below illustrate what the output should look like:

Similar Problems

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Inject Configuration into a Decorator

Decorate a Retryable Operation with Metrics

Add Caching Without Touching Core Logic

Compose Decorators Dynamically Based on Configuration

Add Logging to a Utility Function

Node.js

// Example function
function multiply(a, b) {
  return a * b;
}
// Your code here
// Example usage
const countedMultiply = withCallCount(multiply);
console.log(countedMultiply(2, 3)); // should log count 1
/* Expected output:
[COUNT] Function multiply called 1 times
6 */
console.log(countedMultiply(4, 5)); // should log count 2
/* Expected output:
[COUNT] Function multiply called 2 times
20 */
console.log(countedMultiply(6, 7)); // should log count 3
/* Expected output:
[COUNT] Function multiply called 3 times
42 */