info = {

'name': 'joy',

'age' : 12,

'city': 'Beijing'

}

console.log(info.city)

console.log(info['age'])

for (let key in info) {

console.log(key +' '+ info[key]);

}

class Person{

intro() {

console.log('welcome to js...')

}

}

person = new Person();

person.intro();

const calculator = {

add: function(a, b) {

return a + b;

},

subtract: function(a, b) {

return a - b;

}

};

console.log(calculator.add(5, 3)); // 8

console.log(calculator.subtract(8, 2)); // 6