JavaScript

const obj = {
  a: 1,
  b: function() {
    return this.a;
  }
};
const b = obj.b;
console.log(b());

console.log(0.1 + 0.2 === 0.3);

const obj = { a: 1 };
Object.seal(obj);
obj.b = 2;
console.log(obj.b);

const arr = [1, 2];
arr.length = 0;
console.log(arr[0]);

const obj = {};
Object.defineProperty(obj, "prop", {
  value: 42,
  writable: false
});
obj.prop = 100;
console.log(obj.prop);

const x = (() => {
  try {
    return 10;
  } finally {
    return 20;
  }
})();
console.log(x);

const arr = [1, 2, 3];
arr[-1] = 10;
console.log(arr.length, arr[-1]);

const obj = {
  valueOf: () => 42,
  toString: () => "Hello"
};
console.log(`${obj}`, obj + 10);

console.log([…({ [Symbol.iterator]: function*(){ yield *[1, yield *[2,3] ] } })])

Number.prototype[Symbol.iterator] = function*() { yield *['a','b','c'] };
console.log([...1]);

console.log([..."hello"]);

const obj = {
  a: 1,
  b: 2,
  a: 3
};
console.log(obj.a);

const arr = [1, 2, 3];
arr[10] = 11;
console.log(arr.length);

const name = "Alice";
const obj = {
  name: "Bob",
  getName() {
    return this.name;
  }
};

console.log(obj.getName.call({ name: "Charlie" }));

const sym1 = Symbol("id");
const sym2 = Symbol("id");
console.log(sym1 === sym2);

let name = "Alice";
(function() {
  let name = "Bob";
  console.log(name);
})();
console.log(name);

console.log(typeof typeof 42);

const arr = [1, 2, 3];
const copy = [...arr];
copy.push(4);

console.log(arr);
console.log(copy);

async function test() {
  return (await Promise.resolve(0)) || 10;
}

test().then(console.log);

const obj = { value: 10 };
const result = (obj.value += 5) && obj.value;
console.log(result);

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 () {});

const obj = {
  value: 10,
  getValue: function () {
    return () => this.value;
  }
};

const value = 20;
const getValue = obj.getValue();
console.log(getValue());

function Animal(name) {
  this.name = name;
}
Animal.prototype.sound = 'Generic sound';

const dog = new Animal('Dog');

Animal.prototype.sound = 'Bark';
console.log(dog.sound);

async function test() {
  console.log(1);
  await new Promise(resolve => setTimeout(resolve, 1000));
  console.log(2);
  return 3;
}

console.log(4);
test().then(console.log);
console.log(5);

console.log(typeof NaN);
console.log(NaN === NaN);

function Person(name) {
  this.name = name;
}

Person.prototype.greet = function () {
  console.log(`Hello, ${this.name}`);
};

const person = new Person('Alice');
person.greet();

console.log(person.hasOwnProperty('greet'));

for (var i = 0; i < 3; i++) {
  setTimeout(() => console.log(i), 100);
}

npx is-my-node-vulnerable

const sym = Symbol('unique');
const obj = {
  [sym]: 'Secret',
  public: 'Visible'
};

console.log(Object.keys(obj));
console.log(obj[Symbol('unique')]);

Promise.resolve(1)
  .then(value => {
    console.log(value);
    throw new Error('Something went wrong');
  })
  .then(() => {
    console.log('This will not run');
  })
  .catch(error => {
    console.log('Caught:', error.message);
    return 42;
  })
  .then(value => {
    console.log('Recovered with:', value);
  });

const map = new Map();
const key1 = {};
const key2 = key1;

map.set(key1, "Value for key1");
map.set(key2, "Value for key2");

console.log(map.get({}));
console.log(map.get(key1));

const obj = {};
Object.defineProperty(obj, 'name', {
  value: 'Alice',
  writable: false,
  configurable: false
});

try {
  obj.name = 'Bob';
  delete obj.name;
  console.log(obj.name);
} catch (e) {
  console.log('Error:', e.message);
}

function processData({ a = 10, b = 20 } = { a: 30 }) {
  console.log(a, b);
}

processData({ a: 5 });
processData();

function* numberGenerator() {
  let i = 0;
  while (i < 3) {
    yield i++;
  }
}

const gen = numberGenerator();
console.log(gen.next().value);
console.log(gen.return(10).value);
console.log(gen.next().value);

const obj = Object.freeze({
  name: "Alice",
  info: {
    age: 25
  }
});

try {
  obj.name = "Bob";
  obj.info.age = 30;
} catch (e) {
  console.log("Error:", e.message);
}

console.log(obj.name, obj.info.age);

async function first() {
  console.log('First Start');
  await second();
  console.log('First End');
}

async function second() {
  console.log('Second Start');
}

console.log('Script Start');
first();
setTimeout(() => console.log('Timeout'), 0);
console.log('Script End');