A Date Picker using JavaScript with demo

Here we go to create JavaScript code for A Date Picker

Step 1:
Create Files date.php

<!DOCTYPE html>

<html lang="en">
<head>
  <meta charset="utf-8">
  <title>A Date Chooser</title>
  <script src="dateui.js"></script>
  <script src="datepicker.js"></script>
</head>
<body>
  <h2>A Date Chooser</h2>
  <form id="theForm">
    Year: <input type="text" name="year" id="year" size="4" maxLength="4">
    Month: <select name="month" id="month">
      <option id="month1" value="1">Jan</option>
      <option id="month2" value="2">Feb</option>
      <option id="month3" value="3">Mar</option>
      <option id="month4" value="4">Apr</option>
      <option id="month5" value="5">May</option>
      <option id="month6" value="6">Jun</option>
      <option id="month7" value="7">Jul</option>
      <option id="month8" value="8">Aug</option>
      <option id="month9" value="9">Sep</option>
      <option id="month10" value="10">Oct</option>
      <option id="month11" value="11">Nov</option>
      <option id="month12" value="12">Dec</option>
    </select>
    Day: <select name="day" id="day"></select>&nbsp;
    <input type="text" name="dayInWeek" id="dayInWeek" readonly>&nbsp;
    <input type="button" id="btnNow" value="Now">
  </form>
</body>
</html>

Step 2:
Create dateui.js file

// Dateuijs
// Return true if the given year is a leap year
function isLeapYear(year) {
   return ((year % 4) === 0 && ((year % 100) !== 0 || (year % 400) === 0));
}
 
// Return the number of days in the given month (1-12) of the year (xxxx)
function getDaysInMonth(year, month) {
   if (month === 2) {
      if (isLeapYear(year)) {
         return 29;
      } else {
         return 28;
      }
   } else if ((month === 1) || (month === 3) || (month === 5) || (month === 7)
       || (month === 8) || (month === 10) || (month === 12)) {
      return 31;
   } else {
      return 30;
   }
}
 
// Get the day of the week given year, month (1-12) and day (1-31)
function getDayInWeek(year, month, day) {
  var weekdays = ["Sunday", "Monday", "Tuesday", "Wednesday",
                  "Thursday", "Friday", "Saturday"];
  var theDate = new Date(year, month-1, day);
  return weekdays[theDate.getDay()];
}

Explanation

The function isLeapYear(year) returns true if year is a leap year.

The function getDaysInMonth(year, month) returns the number of days in the given month (1-12) of the year (4-digit). Take note that JavaScript represents a month in the range of 0-11 (for Jan to Dec), instead of 1-12.

The function getDayInWeek(year, month, day) returns the day of the week (Sunday to Saturday). It constructs a built-in object Date with the given year, month and day, and use the getDay() function of the Date object to obtain the day of the week in the range of 0-6.

Step 3:
Create datepicker.js file

window.onload = init;
 
// Global variables for the currently selected year, month and day
var selectedYear;   // 4-digit year
var selectedMonth;  // 1 to 12 for Jan to Dec
var selectedDay;    // 1 to 31
 
// The "onload" handler, runs after the page is fully loaded.
function init() {
   setToday();      // Set global variables
   updateDisplay();
 
   document.getElementById("year").onchange = function() {
      selectedYear=this.value;
      // In case the current day is no longer valid for non-leap year,
      // e.g., 29 Feb 2001. Set to the last year of the month
      updateDayDisplay();
      updateDayInWeekDisplay();
   }
 
   document.getElementById("month").onchange = function() {
      selectedMonth=this.value;
      // In case the current day is no longer valid, e.g., 31 in Feb.
      // Set to the last year of the month
      updateDayDisplay();
      updateDayInWeekDisplay()
   }
 
   document.getElementById("day").onchange = function() {
      selectedDay=this.value;
      updateDayInWeekDisplay();
   }
 
   document.getElementById("btnNow").onclick = function() {
      setToday();
      updateDisplay();
   }
}
 
// Set global variable selectedYear, selectedMonth and selectedDay
// to today.
function setToday() {
   var now = new Date();
   selectedYear = now.getFullYear();   // 4-digit year
   selectedMonth = now.getMonth() + 1; // 1 to 12 for Jan to Dec
   selectedDay = now.getDate();        // 1 to 31
}
 
// Update the year, month, day and day-in-week display according
// to the selected values.
function updateDisplay() {
   // Set the value of text fields and select the correct options
   document.getElementById("year").value = selectedYear;
   updateMonthDisplay();
   updateDayDisplay();
   updateDayInWeekDisplay();
}
 
function updateMonthDisplay() {
   document.getElementById("month" + selectedMonth).selected = true;
}
 
function updateDayDisplay() {
   var elm = document.getElementById("day");
   elm.innerHTML = "";
   var daysInMonth = getDaysInMonth(selectedYear, selectedMonth);
   // The selectedDay is no longer valid. Set to the last day of month
   if (selectedDay > daysInMonth) {
      selectedDay = daysInMonth;
   }
   var options = "";
   for (var day = 1; day <= daysInMonth; day++) {
      options += "<option value='" + day + "'";
      if (day === selectedDay) {
         options += " selected";
      }
      options += ">" + day + "</option>";
   }
   elm.innerHTML = options;
}
 
function updateDayInWeekDisplay() {
   document.getElementById("dayInWeek").value
      = getDayInWeek(selectedYear, selectedMonth, selectedDay);
}

Explanation:
The form consists of 5 input elements: a text field for the year, pull-down menus for month and day, a read-only text field for the day of the week, and a button to set the display to today. When the page is first loaded, the current date is display. If you change the year, month or day, the day of the week changes. If you change the year or month, the options in day adjust automatically, e.g., there are 28/29 days in Feb for non-leap and leap years.

Enjoy the code here

Demo Here –

A Date Picker using JavaScript with demo

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Author: Raja sekar

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