JavaScript - get week number by date (year + month + day)

In this short article, we would like to show how to get current week number for indicated date using JavaScript.

In the example we assume that:

• each week starts on Sunday and ends on Saturday,
• partial weeks are taken into account also (e.g. first and last weeks of year).

Practical example:

// ONLINE-RUNNER:browser;

const getWeekNumber = (year, month, day) => {
    const a = new Date(year, 0, 1);
    const b = new Date(year, month, day);
    return Math.ceil(((b - a) / 86400000 + 1 + a.getDay()) / 7);
};


// Usage example:

// Month: 0 - January, ..., 11 - December

console.log(getWeekNumber(2023, 0, 1));    // 1
console.log(getWeekNumber(2023, 9, 28));   // 43
console.log(getWeekNumber(2023, 11, 31));  // 53