JavaScript: Count the number of days passed since beginning of the year

JavaScript Datetime: Exercise-16 with Solution

Days Passed in Year

Write a JavaScript function to count the number of days passed since the year began.

Test Data:
console.log(days_passed(new Date(2015, 0, 15)));
15
console.log(days_passed(new Date(2015, 11, 14)));
348

Sample Solution:

JavaScript Code:

// Define a JavaScript function called days_passed with parameter dt
function days_passed(dt) {
  // Create a copy of the provided date using getTime() method to avoid modifying the original date
  var current = new Date(dt.getTime());
  // Create a new Date object representing January 1st of the same year as the provided date
  var previous = new Date(dt.getFullYear(), 0, 1);

  // Calculate the difference in milliseconds between the provided date and January 1st
  // Add 1 to consider the current date itself
  // Divide by the number of milliseconds in a day (86400000) to convert milliseconds to days
  // Round up to the nearest whole number using Math.ceil()
  return Math.ceil((current - previous + 1) / 86400000);
}

// Output the number of days passed since January 1st, 2015
console.log(days_passed(new Date(2015, 0, 15)));
// Output the number of days passed since January 1st, 2015 for a different date
console.log(days_passed(new Date(2015, 11, 14)));

Output:

15
348

Explanation:

In the exercise above,

• The code defines a JavaScript function named "days_passed()" with one parameter 'dt', representing a Date object.
• Inside the function:
• It creates a copy of the provided date (dt) using "getTime()" method to avoid modifying the original date, and stores it in the variable 'current'.
• It creates a new Date object named 'previous', representing January 1st of the same year as the provided date (dt).
• It calculates the difference in milliseconds between the provided date and January 1st of the same year, then adds 1 to consider the current date itself.
• It divides the total milliseconds by the number of milliseconds in a day (86400000) to convert milliseconds to days.
• It rounds up the result to the nearest whole number using "Math.ceil()" to get the number of days passed since January 1st of the same year.
• Finally, it returns the calculated number of days passed.
• The code then demonstrates the usage of the "days_passed()" function by calling it with two different dates:
• January 15th, 2015 (new Date(2015, 0, 15))
• December 14th, 2015 (new Date(2015, 11, 14))
• Each console.log() call outputs the number of days passed since January 1st of the respective year to the console.

Flowchart:

Live Demo:

See the Pen JavaScript - Count the number of days passed since beginning of the year-date-ex- 16 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that calculates how many days have passed since January 1st of the current year using the Date object.
• Write a JavaScript function that subtracts January 1st’s timestamp from the current date’s timestamp and divides by the number of milliseconds per day.
• Write a JavaScript function that accounts for leap years when computing the day of the year for a given Date object.
• Write a JavaScript function that validates the input date and returns the day count as an integer.

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