Get the day of the year from a date

JavaScript

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

TypeScript

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

Example

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