JavaScript: Identify a day based on a date

JavaScript Datetime: Exercise-57 with Solution

Day Name from Date String

Write a JavaScript program to get the name of a day based on a given date in string format.

Date format: mm/dd/yyyy

Test Data:
("07/11/2000") -> "Tuesday"
("11/06/2017") -> "Sunday"
("11/26/2017") -> "Not a valid Date!"

Sample Solution:

JavaScript Code:

// Define an array containing names of days of the week
const days_Name = ['Saturday', 'Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
// Define a function to determine the day of the week from a given date string
const Date_To_Day = (dt) => {
  // Check if the input argument is a string
  if (typeof dt !== 'string') {
    return 'Argument should be string!'
  }
  // Extract the day, month, and year from the date string
  let [day, month, year] = dt.split('/').map((x) => Number(x))
  // Check if the date is valid
  if (day < 1 || day > 31 || month > 12 || month < 1) {
    return 'Not a valid Date!'
  }
  // Adjust month and year for calculation
  if (month < 3) {
    year--
    month += 12
  }
  // Calculate the day of the week using Zeller's Congruence formula
  const year_Digits = year % 100
  const century = Math.floor(year / 100)
  const week_Day = (day + Math.floor((month + 1) * 2.6) + year_Digits + Math.floor(year_Digits / 4) + Math.floor(century / 4) + 5 * century) % 7
  // Return the name of the day corresponding to the calculated day of the week
  return days_Name[week_Day] 
}
// Test the function with different date strings and output the result
console.log(Date_To_Day("07/11/2000"))
console.log(Date_To_Day("11/06/2017"))
console.log(Date_To_Day("11/26/2017"))

Output:

Tuesday
Sunday
Not a valid Date! 

Explanation:

In the exercise above,

The code defines a function "Date_To_Day()" that takes a date string in the format "MM/DD/YYYY" as input and returns the corresponding day of the week. The function calculates the day of the week based on the provided date. It first validates the input date string, extracts the day, month, and year, adjusts the month and year if necessary, and then applies the formula to determine the day of the week. Finally, it returns the name of the day (e.g., "Sunday", "Monday") based on the calculated day of the week.

Flowchart:

Live Demo:

See the Pen javascript-date-exercise-57 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that parses a date string and returns the full day name (e.g., "Tuesday") using a lookup array.
• Write a JavaScript function that validates a date string and returns "Not a valid Date!" if the input cannot be parsed.
• Write a JavaScript function that supports multiple date formats and returns the corresponding weekday name.
• Write a JavaScript function that converts a date string to a Date object and then outputs the day name in title case.

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