JavaScript

class CustomError extends Error {
  constructor(message) {
    super(message);
    this.name = this.constructor.name;
  }
}

try {
  throw new CustomError("Something went wrong");
} catch (error) {
  console.log(error.name);
  console.log(error instanceof Error);
  console.log(error instanceof CustomError);
  console.log(typeof error.stack);
}

const cache = new Map();

function memoize(fn) {
  return function(...args) {
    const key = JSON.stringify(args);
    if (cache.has(key)) {
      return cache.get(key);
    }
    const result = fn(...args);
    cache.set(key, result);
    return result;
  };
}

const fibonacci = memoize((n) => {
  if (n <= 1) return n;
  return fibonacci(n - 1) + fibonacci(n - 2);
});

console.log(fibonacci(5));
console.log(cache.size);

const wm = new WeakMap();
const obj1 = { name: 'Sarah' };
const obj2 = { name: 'Mike' };

wm.set(obj1, 'developer');
wm.set(obj2, 'designer');

console.log(wm.get(obj1));
console.log(wm.has(obj2));
console.log(wm.get({ name: 'Sarah' }));
console.log(wm.delete(obj1));
console.log(wm.has(obj1));

class Calculator {
  constructor(value) {
    this.value = value;
  }
  
  add(num) {
    this.value += num;
    return this;
  }
  
  getValue = () => this.value;
}

const calc = new Calculator(10);
const addMethod = calc.add;
const getValueMethod = calc.getValue;

addMethod.call({value: 5}, 3);
console.log(calc.getValue());
console.log(getValueMethod());

const operations = {
  value: 10,
  multiply: function(x) {
    return this.value * x;
  },
  arrow: (x) => {
    return this.value * x;
  },
  nested: function() {
    const inner = () => this.value * 2;
    return inner();
  }
};

console.log(operations.multiply(3));
console.log(operations.arrow(3));
console.log(operations.nested());

console.log('1');

setTimeout(() => console.log('2'), 0);

Promise.resolve().then(() => console.log('3'));

console.log('4');

Promise.resolve().then(() => {
  console.log('5');
  setTimeout(() => console.log('6'), 0);
});

console.log('7');