optional_properies_interface.ts

const start = performance.now();
interface Member {
    name: string;
    birthday?: Date;
    url?: string;
    instrument?: string;
}

const john: Member = {
    name: 'John Lennon',
    url: 'www.johnlennon.com',
};
const paul: Member = {
    name: 'Paul McCartney',
    birthday: new Date('1942-06-18'),
};
const george: Member = {
    name: 'George Harrison',
    instrument: 'guitar',
};
const ringo: Member = {
    name: 'Ringo Starr'
};

const beatles = [john, paul, george, ringo];

for (var i = 0; i < 1000 * 1000 * 1000; i++) {
    beatles[i & 3].name;
}

const end = performance.now();

console.log(end - start);
// V8 7.9.317.31
// 1713.5850000195205
// 1712.8449999727309
// 1678.5799999488518

// Firefox 69
// 46693