JavaScript

const obj = {
  value: 42,
  [Symbol.toPrimitive](hint) {
    if (hint === 'number') return this.value * 2;
    if (hint === 'string') return `Value: ${this.value}`;
    return this.value + 10;
  }
};

console.log(+obj);
console.log(`${obj}`);
console.log(obj + 5);
console.log(Number(obj));

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

const result = numbers
  .map(x => x * 2)
  .filter(x => x > 6)
  .reduce((acc, x) => {
    console.log(`Processing ${x}, acc: ${acc}`);
    return acc + x;
  }, 0);

console.log(`Final result: ${result}`);

const obj = {
  name: 'Calculator',
  values: [1, 2, 3, 4, 5],
  
  regular: function() {
    return this.values.filter(function(x) {
      return x > 2;
    }).length;
  },
  
  arrow: function() {
    return this.values.filter(x => x > 2).length;
  },
  
  broken: () => {
    return this.values.filter(x => x > 2).length;
  }
};

console.log(obj.regular());
console.log(obj.arrow());
try {
  console.log(obj.broken());
} catch(e) {
  console.log('Error');
}

const user = { name: 'Sarah', age: 0 };
const config = { theme: '', debug: false };

const result1 = user.age || 25;
const result2 = user.name && user.name.toUpperCase();
const result3 = config.theme || 'light';
const result4 = config.debug && console.log('Debug mode') || 'disabled';

console.log(result1);
console.log(result2);
console.log(result3);
console.log(result4);

const pipe = (...fns) => (value) => fns.reduce((acc, fn) => fn(acc), value);

const add = (x) => (y) => x + y;
const multiply = (x) => (y) => x * y;
const subtract = (x) => (y) => y - x;

const transform = pipe(
  add(5),
  multiply(3),
  subtract(2)
);

console.log(transform(4));
console.log(transform(0));

class Counter {
  #value = 0;
  
  get count() {
    console.log('Getting count');
    return this.#value;
  }
  
  set count(val) {
    console.log('Setting count to', val);
    this.#value = Math.max(0, val);
  }
}

const counter = new Counter();
counter.count = -5;
console.log(counter.count);

function highlight(strings, ...values) {
  return strings.reduce((result, str, i) => {
    const value = values[i] ? `<em>${values[i]}</em>` : '';
    return result + str + value;
  }, '');
}

const name = 'Sarah';
const score = 95;
const message = highlight`Hello ${name}, your score is ${score}!`;
console.log(message);