Advanced Functional Patterns

Preview — 3 of 10 questions

Which of the following best describes a transducer in JavaScript?

javascript

const numbers = [1, 2, 3, 4, 5];

const result = numbers
  .filter(x => x % 2 === 0) // [2, 4] - intermediate array
  .map(x => x * 2) // [4, 8] - another intermediate array
  .reduce((sum, x) => sum + x, 0); // 12

// Two intermediate arrays created

AA function that reduces an array to a single value.

BA higher-order function that transforms a reducer function to improve performance.

CA function that maps an array to a new array without side effects.

DA function that composes multiple reducers together.

What is the main advantage of lazy evaluation in functional programming?

javascript

function getExpensiveValue() {
  console.log("Computing...");
  return Array.from({ length: 1000000 }, (_, i) => i);
}

function process(data) {
  const result = data.filter(x => x > 100); // Processes all 1M items
  return result.slice(0, 5); // But only returns first 5
}

process(getExpensiveValue()); // Wastes computation

AIt allows immediate execution of all function calls.

BIt defers computation until the result is actually needed, improving performance.

CIt makes debugging easier by executing all functions eagerly.

DIt prevents all side effects in JavaScript.

Which of the following optimizations can improve the performance of a recursive function?

javascript

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

fibonacci(40); // Very slow! Calculates fibonacci(39), fibonacci(38), etc. multiple times

AMemoization

BUsing a for-loop instead of recursion

CCalling the function synchronously in a loop

DIncreasing the recursion depth

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