Below I am sharing a demo code: JSFiddle - Code Playground

and also the full code:

Demo: https://jsfiddle.net/u5jh6wg2/




    
    
    
    
    



    

    
Date Picker Demo
    
Select a date between the minimum date and 30-Apr-2025.

        Installation Date:
        
    

    
    
    

Part -1

To enable future dates up to 30-Apr-2025 in your date picker, you need to check that the maxDate option is set correctly. In your code, you are already setting maxDate to currentDate, which is defined as new Date("30/Apr/2025"). 

// Get the minimum date from the hidden field
var minimumdate = document.getElementById("PageContent_hdnVdate").value;

// Set the maximum date to 30-Apr-2025
var currentDate = new Date("2025-04-30"); // Use ISO format (YYYY-MM-DD) for better compatibility

// Initialize the date picker
function GetRestart1() {
    $("#<%=txt_installationDate.ClientID %>").datepicker({
        changeMonth: true, // Allow changing months
        changeYear: true,  // Allow changing years
        dateFormat: "dd/M/yy", // Set the date format
        maxDate: currentDate, // Set the maximum selectable date
        minDate: minimumdate, // Set the minimum selectable date
        showOn: "both", // Show the date picker on both button and input field click
        buttonImage: "../img/calendar.png", // Set the calendar icon
        buttonImageOnly: true, // Show only the icon, not the text
        onClose: function (selectedDate) {
            // Update the minimum date for other date pickers if needed
            $("#<%=txt_installationDate.ClientID %>").datepicker("option", "minDate", selectedDate);
        }
    });
}

1. Date Format for currentDate:

   • Changed new Date("30/Apr/2025") to new Date("2025-04-30").

   • The ISO format (YYYY-MM-DD) is more reliable across different browsers and environments.

2. showOn Option:

   • You had showOn: "button" and showOn: "both" duplicated. I kept showOn: "both" to check the date picker shows on both the input field and the button click.

3. onClose Function:

   • This function updates the minDate for other date pickers if needed. If you don’t have other date pickers to synchronize, you can remove this part.

I think your issue is how the currentDate is being set. The new Date("30/Apr/2025") syntax may not work as expected due to potential inconsistencies in parsing date formats across browsers.

var minimumdate = document.getElementById("PageContent_hdnVdate").value;
var currentDate = new Date(2025, 3, 30); 

function GetRestart1() {
    $("#<%=txt_installationDate.ClientID %>").datepicker({
        changeMonth: true,
        changeYear: true,
        dateFormat: "dd/M/yy",
        maxDate: currentDate,
        minDate: new Date(minimumdate),
        showOn: "button",
        buttonImage: "../img/calendar.png",
        buttonImageOnly: true,
        onClose: function (selectedDate) {
            $("#<%=txt_installationDate.ClientID %>").datepicker("option", "minDate", selectedDate);
        }
    });
}