JavaScript

const factorial = (function () {
  const cache = {};
  return function inner(n) {
    if (n in cache) return cache[n];
    return (cache[n] = n <= 1 ? 1 : n * inner(n - 1));
  };
})();

console.log(factorial(5)); 
console.log(factorial(5));

function Person(name) {
  this.name = name;
  this.sayName = () => console.log(this.name);
}

const person1 = new Person('David');
const person2 = { name: 'Not David', sayName: person1.sayName };

person2.sayName();

const a = false || 0 || "" || null || "JavaScript";
console.log(a);

const obj = { a: 10 };
console.log(obj.a && obj.b || 20);

function memoize(fn) {
  const cache = {};
  return (arg) => cache[arg] ?? (cache[arg] = fn(arg));
}

const square = memoize((n) => n * n);

console.log(square(5)); 
console.log(square(5)); 
console.log(square(6));

console.log('A');

setTimeout(() => console.log('B'), 0);

Promise.resolve()
  .then(() => {
    console.log('C');
    return Promise.resolve();
  })
  .then(() => console.log('D'));

console.log('E');

console.log(typeof null);
console.log(typeof function () {});