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BRUCE_FE JS Interview Notes - Implementing Memoize Function

Learn how to implement JavaScript memoization functions, improve function execution efficiency, avoid repeated calculations, and master caching strategies and their applications in frontend development.

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What is Memoize

Memoization is an optimization technique that speeds up program execution by storing the results of expensive function calls and returning cached results when the same inputs occur again. It's mainly applicable to pure functions in functional programming (same input always produces same output).

Core Concepts of Memoization

1. Cache Results: Store function call results
2. Cache Hit: Return previously calculated results when same parameters are called again
3. Pure Functions: Functions with no side effects and output determined only by input, suitable for memoization
4. Performance Optimization: Significantly reduce time cost of repeated calculations

Implementing Basic Memoize Function

Below is a basic memoize function implementation that can memorize results of any pure function:

function memoize(fn) {
  // Create cache object
  const cache = {};
  
  // Return a new function
  return function(...args) {
    // Convert parameters to string as key
    const key = JSON.stringify(args);
    
    // Check if result exists in cache
    if (key in cache) {
      console.log('Returning result from cache');
      return cache[key];
    }
    
    // If no cache, call original function to calculate result
    const result = fn.apply(this, args);
    
    // Store result in cache
    cache[key] = result;
    
    return result;
  };
}

Usage Example

// Calculate Fibonacci sequence
function fibonacci(n) {
  if (n <= 1) return n;
  return fibonacci(n - 1) + fibonacci(n - 2);
}

// Non-memoized function call (poor performance)
console.time('Non-memoized');
console.log(fibonacci(35)); // This will take a long time
console.timeEnd('Non-memoized');

// Memoized version
const memoizedFibonacci = memoize(function(n) {
  if (n <= 1) return n;
  return memoizedFibonacci(n - 1) + memoizedFibonacci(n - 2);
});

// Memoized function call (significantly improved performance)
console.time('Memoized');
console.log(memoizedFibonacci(35)); // Returns result quickly
console.timeEnd('Memoized');