List of examples on how you can use and benchmark JS iterators

iterators.js

// ECMAScript 2025 Iterator Examples
// New built-in Iterator global with functional operators

// Example 1: Working with Arrays using Iterator helpers
const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

const result = Iterator.from(numbers)
  .filter(x => x % 2 === 0)  // Keep even numbers
  .map(x => x * x)           // Square them
  .take(3)                   // Take first 3
  .toArray();                // Convert back to array

console.log(result); // [4, 16, 36]

// Example 2: Working with Generator Functions
function* fibonacci() {
  let a = 0, b = 1;
  while (true) {
    yield a;
    [a, b] = [b, a + b];
  }
}

const fibNumbers = Iterator.from(fibonacci())
  .take(10)                  // Take first 10 fibonacci numbers
  .filter(x => x > 5)        // Filter numbers greater than 5
  .map(x => `Fib: ${x}`)     // Format them
  .toArray();

console.log(fibNumbers); // ["Fib: 8", "Fib: 13", "Fib: 21", "Fib: 34"]

// Example 3: Lazy Evaluation - Processing Large Datasets
function* generateLargeDataset() {
  for (let i = 1; i <= 1000000; i++) {
    yield { id: i, value: Math.random() * 100 };
  }
}

// This is memory efficient - no intermediate arrays created
const processedData = Iterator.from(generateLargeDataset())
  .filter(item => item.value > 50)
  .map(item => ({ ...item, processed: true }))
  .take(5)
  .toArray();

console.log(processedData);

// Example 4: Working with Strings
const text = "Hello World JavaScript";
const processed = Iterator.from(text)
  .filter(char => char !== ' ')
  .map(char => char.toUpperCase())
  .take(10)
  .toArray()
  .join('');

console.log(processed); // "HELLOWORLD"

// Example 5: Chaining Multiple Operations
const users = [
  { name: "Alice", age: 25, active: true },
  { name: "Bob", age: 30, active: false },
  { name: "Charlie", age: 35, active: true },
  { name: "Diana", age: 28, active: true },
  { name: "Eve", age: 32, active: false }
];

const activeUserNames = Iterator.from(users)
  .filter(user => user.active)
  .filter(user => user.age > 25)
  .map(user => user.name.toUpperCase())
  .toArray();

console.log(activeUserNames); // ["CHARLIE", "DIANA"]

// Example 6: Drop and Take for Pagination-like Behavior
const items = Array.from({ length: 100 }, (_, i) => `Item ${i + 1}`);

const page2Items = Iterator.from(items)
  .drop(10)    // Skip first 10 items (page 1)
  .take(10)    // Take next 10 items (page 2)
  .toArray();

console.log(page2Items); // ["Item 11", "Item 12", ..., "Item 20"]

// Example 7: Performance Comparison
console.time('Array methods');
const arrayResult = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  .filter(x => x % 2 === 0)
  .map(x => x * x)
  .slice(0, 3);
console.timeEnd('Array methods');

console.time('Iterator methods');
const iteratorResult = Iterator.from([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
  .filter(x => x % 2 === 0)
  .map(x => x * x)
  .take(3)
  .toArray();
console.timeEnd('Iterator methods');

// Both produce the same result, but Iterator methods are more memory efficient
console.log('Array result:', arrayResult);
console.log('Iterator result:', iteratorResult);