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Grokking Node.js Design Patterns for Interviews

Problem: Measure Execution Time for an Async Task

Easy
15 min
Wrap an asynchronous function with a decorator that measures and logs how long it takes to complete.

Problem statement

You’re simulating a service call that takes some time to complete, maybe fetching data from a database or an external API. You need to measure how long this operation takes, but you can’t alter the service function directly. You’ll use a decorator to wrap it, measure its duration, and log the timing details.

Goal

Create a withTiming decorator that:

  • Measures how long the wrapped async function takes to resolve.

  • Logs the duration in milliseconds.

  • Returns the original function’s result.

Constraints

  • Do not modify the original async function.

  • The decorator should log the time after the function completes.

  • Do not use any external libraries for timing.

Sample output

The examples below illustrate what the output should look like:

const timedFetch = withTiming(fetchUser);
(async () => {
  await timedFetch(42); // should log how long it took
  await timedFetch(7);  // should log again
})();
/* Expected output (might vary):
[TIMER] fetchUser took 103ms
[TIMER] fetchUser took 99ms */

Good luck trying the problem! If you’re unsure how to proceed, check the “Solution” tab above.

Similar Problems
Decorate a Retryable Operation with Metrics
Add Caching Without Touching Core Logic
Compose Decorators Dynamically Based on Configuration
Add Logging to a Utility Function
Chain Multiple Decorators on a Service Method
Add Authorization to a Route Handler
Inject Configuration into a Decorator
Track Function Call Count with a Decorator
Home
Courses
Grokking Node.js Design Patterns for Interviews

Problem: Measure Execution Time for an Async Task

Easy
15 min
Wrap an asynchronous function with a decorator that measures and logs how long it takes to complete.

Problem statement

You’re simulating a service call that takes some time to complete, maybe fetching data from a database or an external API. You need to measure how long this operation takes, but you can’t alter the service function directly. You’ll use a decorator to wrap it, measure its duration, and log the timing details.

Goal

Create a withTiming decorator that:

  • Measures how long the wrapped async function takes to resolve.

  • Logs the duration in milliseconds.

  • Returns the original function’s result.

Constraints

  • Do not modify the original async function.

  • The decorator should log the time after the function completes.

  • Do not use any external libraries for timing.

Sample output

The examples below illustrate what the output should look like:

const timedFetch = withTiming(fetchUser);
(async () => {
  await timedFetch(42); // should log how long it took
  await timedFetch(7);  // should log again
})();
/* Expected output (might vary):
[TIMER] fetchUser took 103ms
[TIMER] fetchUser took 99ms */

Good luck trying the problem! If you’re unsure how to proceed, check the “Solution” tab above.

Similar Problems
Decorate a Retryable Operation with Metrics
Add Caching Without Touching Core Logic
Compose Decorators Dynamically Based on Configuration
Add Logging to a Utility Function
Chain Multiple Decorators on a Service Method
Add Authorization to a Route Handler
Inject Configuration into a Decorator
Track Function Call Count with a Decorator
Node.js
// Simulated async service
async function fetchUser(id) {
  return new Promise((resolve) => {
    setTimeout(() => resolve({ id, name: 'Alice' }), 100);
  });
}
// Your code here
// Example usage
const timedFetch = withTiming(fetchUser);
(async () => {
  await timedFetch(42); // should log how long it took
  await timedFetch(7);  // should log again
})();
/* Expected output:
[TIMER] fetchUser took 103ms
[TIMER] fetchUser took 99ms */