Get the day of the year from a date

// `date` is a Date object
const dayOfYear = (date) => Math.floor((date - new Date(date.getFullYear(), 0, 0)) / (1000 * 60 * 60 * 24));

const dayOfYear = (date: Date): number =>
    Math.floor((date.valueOf() - new Date(date.getFullYear(), 0, 0).valueOf()) / (1000 * 60 * 60 * 24));

dayOfYear(new Date(2020, 04, 16)); // 137