JS Built-ins
← DesignPatterns17 / 25
DesignPatternsbeginner

Decorator — Timed function

📖 Usage Example
function timed(fn) {
  return function(...args) {
    const start = Date.now();
    const result = fn.apply(this, args);
    console.log(Date.now() - start, 'ms');
    return result;
  };
}

A timing decorator measures how long a function takes to execute.

Decorator Pattern — Timing Execution

A decorator can measure and track function execution time.

Challenge: Implement a timed(fn) decorator that wraps a function. The wrapper should:

  • Call the original function
  • Return the result unchanged

(The timing behavior is internal; we're testing that the result is correct)

Example:

const slow = (x) => x * 2
const timedSlow = timed(slow)
timedSlow(5) // returns 10
💡 Hints (3)
  • • Capture the start time
  • • Call the original function
  • • Return the result from the original function