Transform values from a JSON representation

const person = {
    name: 'John Doe',
    ages: 42,
    phones: new Set(['123', '456', '789']),
};

JSON.stringify(person);

// "{"name":"John Doe","ages":42,"phones":{}}"

JSON.stringify(variable, (key, value) => {
    // The return value will be used in final output

    // If the function returns `undefined`,
    // the item will be excluded from the output
    return ...;
});

JSON.stringify(person, (key, value) => (key === 'phones' ? [...value.values()] : value));

// "{"name":"John Doe","ages":42,"phones":["123","456","789"]}"

JSON.stringify(person, (key, value) => (value instanceof Set ? [...value.values()] : value));