JavaScript

const obj = {
  name: 'Taylor',
  greet() {
    return `Hello, ${this.name}!`;
  },
  delayedGreet() {
    setTimeout(function() {
      console.log(this.greet());
    }, 100);
  }
};

obj.delayedGreet();

function* rangeGenerator(start, end, step = 1) {
  let current = start;
  while (current <= end) {
    yield current;
    current += step;
  }
}

const numbers = rangeGenerator(1, 10, 2);

numbers.next();
numbers.next();

const values = [...numbers];
console.log(values);

function outer() {
  console.log(innerVar);
  console.log(typeof innerFunc);
  
  var innerVar = 42;
  
  function innerFunc() {
    return innerVar;
  }
  
  let anotherVar = 100;
  console.log(typeof anotherVar);
}

outer();

async function fetchData() {
  return 'Data loaded';
}

async function processData() {
  console.log('Starting...');
  try {
    const result = fetchData();
    console.log(result);
    console.log(await result);
    return 'Processing complete';
  } catch (error) {
    return 'Error occurred';
  } finally {
    console.log('Cleanup');
  }
}

processData().then(result => console.log(result));

const cache = new WeakMap();

function expensiveOperation(obj) {
  if (cache.has(obj)) {
    console.log('Cache hit!');
    return cache.get(obj);
  }
  
  console.log('Computing result...');
  const result = obj.value * 2;
  cache.set(obj, result);
  return result;
}

const user = { value: 42 };
expensiveOperation(user);
expensiveOperation(user);
expensiveOperation({ value: 42 });

function processUserData(data) {
  try {
    if (!data) {
      throw new Error('No data provided');
    }
    
    if (!data.name) {
      throw new TypeError('Name is required');
    }
    
    return { success: true, user: data.name };
  } catch (err) {
    if (err instanceof TypeError) {
      return { success: false, reason: 'validation-failed' };
    }
    return { success: false, reason: 'unknown-error' };
  }
}

console.log(processUserData({}));

function createCounter() {
  let count = 0;
  
  function increment() {
    count++;
    return count;
  }
  
  function decrement() {
    count--;
    return count;
  }
  
  return { increment, decrement, reset: () => count = 0 };
}

const counter = createCounter();
counter.increment();
counter.increment();
counter.decrement();

const { increment, reset } = counter;
increment();
reset();
increment();

console.log(counter.increment());

const map = new WeakMap();

let obj1 = { name: 'user1' };
let obj2 = { name: 'user2' };

map.set(obj1, 'data for user1');
map.set(obj2, 'data for user2');

console.log(map.has(obj1));
obj1 = null;

// After garbage collection runs
console.log(map.has(obj1));
console.log(map.get(obj2));