JavaScript: Find out the last day of a month

JavaScript Datetime: Exercise-9 with Solution

Last Day of Month

Write a JavaScript function to get the last day of a month.

Test Data:
console.log(lastday(2014,0));
console.log(lastday(2014,1));
console.log(lastday(2014,11));
Output :
31
28
31

Sample Solution:

JavaScript Code:

// Define a JavaScript function called lastday with parameters y (year) and m (month)
var lastday = function(y, m){
    // Create a new Date object representing the last day of the specified month
    // By passing m + 1 as the month parameter and 0 as the day parameter, it represents the last day of the specified month
    return new Date(y, m + 1, 0).getDate();
}

// Output the last day of January 2014
console.log(lastday(2014, 0));
// Output the last day of February 2014
console.log(lastday(2014, 1));
// Output the last day of December 2014
console.log(lastday(2014, 11));

Output:

31
28
31

Explanation:

In the exercise above,

• The code defines a JavaScript function named "lastday()" with two parameters: 'y' for the year and 'm' for the month.
• Inside the function:
• It creates a new Date object representing the last day of the specified month and year.
• To find the last day of the month, it sets the month parameter to 'm + 1' (next month) and the day parameter to '0'. JavaScript handles this by rolling back to the last day of the previous month.
• It retrieves the day component of the resulting Date object using the "getDate()" method, which returns the day of the month (1 to 31).
• The function returns the last day of the specified month as an integer.
• The code then demonstrates the "lastday()" function by calling it with three different month and year combinations:
• January 2014
• February 2014
• December 2014

Flowchart:

Live Demo:

See the Pen JavaScript - Find out the last day of a month-date-ex- 9 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that returns the last day of a given month by setting the date to 0 of the following month.
• Write a JavaScript function that handles leap year logic for February and returns the correct last day.
• Write a JavaScript function that accepts month and year as parameters, validates them, and outputs the final day of that month.
• Write a JavaScript function that compares computed last days of different months for verification.

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