const nums = [1, 2, 3, 4, 5];
const result = nums
  .filter(n => n > 2)
  .map(n => n * 2)
  .reduce((acc, n) => {
    acc.push(n + 1);
    return acc;
  }, [])
  .slice(1);

console.log(result);
console.log(nums);

function* generator1() {
  yield 1;
  yield 2;
}

function* generator2() {
  yield* generator1();
  yield 3;
}

const gen = generator2();
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next().value);

const sym1 = Symbol('test');
const sym2 = Symbol('test');
const obj = {
  [sym1]: 'value1',
  [sym2]: 'value2',
  regular: 'value3'
};

const sym3 = Symbol.for('global');
const sym4 = Symbol.for('global');

console.log(sym1 === sym2);
console.log(sym3 === sym4);
console.log(Object.keys(obj).length);
console.log(Object.getOwnPropertySymbols(obj).length);

const regex = /\d{2,}/;
console.log(regex.test('5'), regex.test('55'), regex.test('555'));

function Person(name) {
  this.name = name;
}
Person.prototype.greet = function() {
  return `Hello, my name is ${this.name}`;
};
const john = new Person('John');
console.log(john.greet());

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

outer();

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

try {
  throw new CustomError('Something went wrong', 500);
} catch (error) {
  console.log(error instanceof Error);
  console.log(error instanceof CustomError);
  console.log(error.name);
  console.log(typeof error.code);
}

const arr = [1, 2, 3, 4, 5];
const result = arr
  .map(x => x * 2)
  .filter(x => x > 5)
  .reduce((acc, val) => {
    return acc + (val % 3 === 0 ? val : 0);
  }, 0);

console.log(result);

console.log('Start');

setTimeout(() => {
  console.log('Timeout 1');
}, 0);

Promise.resolve().then(() => {
  console.log('Promise 1');
}).then(() => {
  console.log('Promise 2');
});

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

console.log('End');

class StateMachine {
  constructor() {
    this.state = 'idle';
    this.transitions = {
      idle: { start: 'running', reset: 'idle' },
      running: { pause: 'paused', stop: 'stopped' },
      paused: { resume: 'running', stop: 'stopped' },
      stopped: { reset: 'idle' }
    };
  }
  
  transition(action) {
    const nextState = this.transitions[this.state]?.[action];
    if (nextState) {
      this.state = nextState;
      return true;
    }
    return false;
  }
}

const sm = new StateMachine();
console.log(sm.transition('start'));
console.log(sm.state);
console.log(sm.transition('reset'));
console.log(sm.state);

const target = { name: 'Sarah', age: 25 };
const handler = {
  get(obj, prop) {
    if (prop === 'toString') {
      return () => `Person: ${obj.name}`;
    }
    return Reflect.get(obj, prop);
  },
  has(obj, prop) {
    return prop !== 'age' && Reflect.has(obj, prop);
  }
};
const proxy = new Proxy(target, handler);
console.log(proxy.name);
console.log('age' in proxy);
console.log(proxy.toString());

const numbers = [1, 2, 3, 4, 5, 6];

const result = numbers.reduce((acc, num) => {
  if (num % 2 === 0) {
    acc.even += num;
  } else {
    acc.odd *= num;
  }
  return acc;
}, { even: 1, odd: 1 });

console.log(result);

const matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
];

let columnSums = [];

for (let i = 0; i < matrix[0].length; i++) {
  let sum = 0;
  for (let j = 0; j < matrix.length; j++) {
    sum += matrix[i][i];
  }
  columnSums.push(sum);
}
console.log(columnSums);

const arr = [1, 2, 3];
const str = arr.join([4]);
console.log(typeof str);
console.log(str);

var arr = Array.from({ length: 5 }, (v, i) => i * 2);
console.log(arr);

function main() {
  console.log(1);
  
  setTimeout(() => console.log(2), 0);
  
  Promise.resolve().then(() => {
    console.log(3);
    setTimeout(() => console.log(4), 0);
  }).then(() => console.log(5));
  
  Promise.resolve().then(() => console.log(6));
  
  console.log(7);
}

main();

const cache = new WeakMap();
const obj1 = { id: 1 };
const obj2 = { id: 2 };

cache.set(obj1, 'data1');
cache.set(obj2, 'data2');

obj2.newProp = 'test';

console.log(cache.has(obj1), cache.has(obj2), cache.has({ id: 1 }));

const obj = { length: 3 };
console.log(Object.keys(obj).length);

console.log('1');

Promise.resolve().then(() => {
  console.log('2');
  Promise.resolve().then(() => console.log('3'));
});

Promise.resolve().then(() => {
  console.log('4');
});

setTimeout(() => console.log('5'), 0);

console.log('6');

var str="good wood food cat bat hat";
console.log( str.match(/((g|w|f)ood)|((c|b|h)at)/g) );