I've recently been introduced to the Intl object, which is used as the namespace for the ECMAScript Internationalization API. It has a neat object called DateTimeFormat which can be used to format a date value into locale specific strings.

I'll show you a typical use case for using Intl.DateTimeFormat to generate the weekday of a given date string (e.g. 07/16/1945).

Problem

Given a dateString in the format MM/DD/YYYY, find and return the weekday for that date.

Solution

/**
 * Given a date string in the format MM/DD/YYY, find and return the 
 * weekday for that date in English.
 *
 * @param {string} dateString
 * @returns {string} - weekday for the given date [e.g: Wednesday]
 */
const getWeekDay = (dateString) => {
  const date = new Date(dateString);
  const dateTimeFormatOptions = { weekday: 'long' };
  const dateTimeFormat = new Intl.DateTimeFormat('en-US', dateTimeFormatOptions); 
  return dateTimeFormat.format(date);
}

Explanation

1. Create a function expression called getWeekDay which takes a string (dateString).
2. Create a Date object with the given dateString, so that we can pass it as a parameter into the format method of DateTimeFormat.
3. Create an object to hold the options parameter for Intl.DateTimeFormat. Setting the weekday property equals to long, so that we get the localized weekday when calling format.
4. Create a an instance of Intl.DateTimeFormat setting locales to en-US, and passing in the previously created dateTimeFormatOptions object.
5. Return the result of calling format method on Intl.DateTimeFormat to find the weekday for the given date.

Output

console.log(getWeekDay("07/16/1945"));
// expected output: "Monday"

In closing, we used the Intl.DateTimeFormat object to quickly find the weekday of a given date string. Best of all Intl has great support across modern browser.

Thank you for reading.