JavaScript: Get ISO-8601 numeric representation of the day of the week

JavaScript Datetime: Exercise-22 with Solution

ISO Weekday Number

Write a JavaScript function to get an ISO-8601 numeric representation of the day of the week (1 (for Monday) to 7 (for Sunday).

Test Data :
dt = new Date();
console.log(ISO_numeric_date(dt));
4
dt = new Date(2015, 10, 1);
console.log(ISO_numeric_date(dt));
7

Sample Solution:

JavaScript Code:

// Define a function ISO_numeric_date that takes a Date object dt as input
function ISO_numeric_date(dt)
{
  // Return the day of the week for the provided date, represented as a numeric value
  // If the day is Sunday (0), return 7 instead to conform to ISO 8601 standard
  return (dt.getDay() === 0 ? 7 : dt.getDay());
}
// Create a new Date object representing the current date
dt = new Date();
// Output the numeric representation of the day of the week using ISO 8601 standard for the current date
console.log(ISO_numeric_date(dt));
// Create a new Date object representing November 1, 2015
dt = new Date(2015, 10, 1);
// Output the numeric representation of the day of the week using ISO 8601 standard for November 1, 2015
console.log(ISO_numeric_date(dt));

Output:

2
7

Explanation:

In the exercise above,

• The code defines a function named "ISO_numeric_date()" that takes a Date object dt as input.
• Inside the ISO_numeric_date function:
• It checks if the day of the week for the provided date (dt.getDay()) is equal to 0, which represents Sunday.
• If the day is Sunday (0), it returns 7 instead. This adjustment is made to conform to the ISO 8601 standard, where Monday is considered the first day of the week and is represented by 1.
• After defining the function, the code creates a new Date object "dt" representing the current date using 'new Date()'. It then calls the "ISO_numeric_date()" function with this Date object and outputs the result to the console.
• Next, the code creates another new Date object "dt" representing November 1, 2015, using 'new Date(2015, 10, 1)'. It again calls the "ISO_numeric_date()" function with this Date object and outputs the result to the console.

Flowchart:

Live Demo:

See the Pen JavaScript - Get ISO-8601 numeric representation of the day of the week-date-ex-22 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that returns the ISO-8601 numeric representation of the weekday (1 for Monday to 7 for Sunday) from a Date object.
• Write a JavaScript function that adjusts the standard getDay() value to conform to the ISO standard.
• Write a JavaScript function that converts a date string to a Date object and returns its ISO weekday number.
• Write a JavaScript function that validates the date input and returns a default value if the date is invalid.

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