Week of Year

Introduction

In this lab, we will explore how to calculate the zero-indexed week of the year that a given date corresponds to using JavaScript. We will use the Date constructor and several Date.prototype methods to obtain the first Monday of the year and calculate the number of weeks between the first Monday and the given date. This lab is designed to enhance your understanding of JavaScript date manipulation and calculation.

Skills Graph

Obtaining the Week of Year from a Date in JavaScript

To obtain the zero-indexed week of the year that corresponds to a date in JavaScript, follow these steps:

1. Create a weekOfYear function that takes a date parameter.
2. Use the Date constructor and Date.prototype.getFullYear() to get the first day of the year as a Date object.
3. Use Date.prototype.setDate(), Date.prototype.getDate() and Date.prototype.getDay() along with the modulo (%) operator to get the first Monday of the year.
4. Subtract the first Monday of the year from the given date and divide with the number of milliseconds in a week.
5. Use Math.round() to get the zero-indexed week of the year corresponding to the given date.
6. If the given date is before the first Monday of the year, -0 is returned.

Here's the code:

const weekOfYear = (date) => {
  const startOfYear = new Date(date.getFullYear(), 0, 1);
  startOfYear.setDate(startOfYear.getDate() + (startOfYear.getDay() % 7));
  return Math.round((date - startOfYear) / (7 * 24 * 3600 * 1000));
};

To use the weekOfYear function, simply call it with a Date object as its parameter:

weekOfYear(new Date("2021-06-18")); // 23

This will return the zero-indexed week of the year that corresponds to the given date, which in this case is 23.

Summary

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