Correct JS

can you paste the code as codes instead of image here?

You are missing a closing } to close the anonymous function on the change event

The second to last line should be }}) to close the if statement and the function declaration.

Thanks to all.
Jeffrey,
By that part of JS codes, I want to disable button below (when readonly=y)

but it cannot do that below. What to adjust?
http://my-friend.co/UserMaintenance2/Default.aspx?userid=mc4&readonly=y

I guess this code you need to write on document.ready

var isreadonly = getUrlParameter('readonly');
        if (isreadonly == "y") {
            $("#tb_birth").datepicker("disable");
        }

Select allOpen in new window

Is it to put such codes to Java script in above? How to adjust the above codes? Where is document.ready?

What you are trying to do is fine. I meant the syntax of your JavaScript is incorrect.
At the end it should be

        if (isreadonly == "y") {
            $("#tb_birth").datepicker("disable");
        }})

Select allOpen in new window

See how I added an extra }, that is to close the function you opened earlier

Yes, I have codes like

$(function () {
    $("#tb_birth").datepicker({
        dateFormat: "dd/mm/yy",
        changeYear: true,
        showOn: "button",
    }).next('button').text('').button({
        icons: {
            primary: 'ui-icon-calendar'
        },
        label: "选择日期",
        text: false
    }).on("change", function () {
        var isreadonly = getUrlParameter('readonly');
        if (isreadonly == "y") {
            $("#mybutton").attr("disabled", "disabled")
        }
        var isreadonly = getUrlParameter('readonly');
        if (isreadonly == "y") {
            $("#tb_birth").datepicker("disable");
        }
    });
    });

Select allOpen in new window

but after deployment, I still cannot disable the button next to date field below.

http://my-friend.co/UserMaintenance2/Default.aspx?userid=mc4&readonly=y

Firstly you have this

var isreadonly = getUrlParameter('readonly');

Select allOpen in new window

Which is INSIDE the .on("change") so the check for readonly is only going to happen when you actually change the date.

If you want to disable the button based on the URL parameter at page load you have to move this OUTSIDE of the function chain you have going

Then you can optimise your code to do this

// ONLY GET THIS ONCE
 var isreadonly = getUrlParameter('readonly');
if (isreadonly == "y") {
  // USE prop RATHER THAN attr AND SET IT TO TRUE
  $("#mybutton").prop("disabled", true)
 // DISABLE THE DATEPICKER
  $("#tb_birth").datepicker("option", { disabled: true });
}

Select allOpen in new window

However, we can make this even simpler. Firstly, there is no id="mybutton" in your code so that line is totally useless.
Secondly, if you disable the datepicker the button will no longer open the DatePicker and is effectively disabled. You can therefore just do this

$(function() {
  // ONLY GET THIS ONCE
 var isreadonly = getUrlParameter('readonly');
  if (isreadonly == "y") {
    // DISABLE THE DATEPICKER
    $("#tb_birth").datepicker("option", { disabled: true });
  }
})

Select allOpen in new window

If you want to disable the button then use the first code listing making sure you reference an id that actually exists in your page.

Some things to remember

When disabling controls use .prop() and remember that disabled is a Boolean and should be set to true or false.

Thanks to all.
Julian,
Here is the current codes

$(function () {
    $("#tb_birth").datepicker({
        dateFormat: "dd/mm/yy",
        changeYear: true,
        showOn: "button",
    }).next('button').text('').button({
        icons: {
            primary: 'ui-icon-calendar'
        },
        label: "选择日期",
        text: false
    }).on("change", function () {
        var isreadonly = getUrlParameter('readonly');
        if (isreadonly == "y") {
            // DISABLE THE DATEPICKER
            $("#tb_birth").datepicker("option", { disabled: true });
        }
    });
});

Select allOpen in new window

but I still cannot disable the datepicker, after re-deployment, below.

http://my-friend.co/UserMaintenance2/Default.aspx?userid=mc4&readonly=y

Please read my previous comment

YOU ARE PUTTING YOUR DISABLE CODE INSIDE AN ONCHANGE

}).on("change", function () {
 // ************************************
 // THIS CODE WILL ONLY FIRE WHEN YOU CHANGE THE VALUE IN THE DATEPICKER - IS THIS WHAT YOU WANT?
 // ************************************
        var isreadonly = getUrlParameter('readonly');
        if (isreadonly == "y") {
            // DISABLE THE DATEPICKER
            $("#tb_birth").datepicker("option", { disabled: true });
        }
    });

Select allOpen in new window

How to ensure to "get your codes once"?

I don't understand the question.

Per your advice

// ONLY GET THIS ONCE
 var isreadonly = getUrlParameter('readonly');
if (isreadonly == "y") {
  // USE prop RATHER THAN attr AND SET IT TO TRUE
  $("#mybutton").prop("disabled", true)
 // DISABLE THE DATEPICKER
  $("#tb_birth").datepicker("option", { disabled: true });
}

what do you mean by

"ONLY GET THIS ONCE"?

In your original code you had

}).on("change", function () {
       // THIS LINE IS IDENTICAL ....
        var isreadonly = getUrlParameter('readonly');
        if (isreadonly == "y") {
            $("#mybutton").attr("disabled", "disabled")
        }
       // TO THIS ONE. 
       // THIS LINE IS UNNECESSARY - YOU ALREADY HAVE THIS VALUE ABOVE
        var isreadonly = getUrlParameter('readonly');
        if (isreadonly == "y") {
            $("#tb_birth").datepicker("disable");
        }
    });
    });

Select allOpen in new window

Using these codes

$(function () {
    $("#tb_birth").datepicker({
        dateFormat: "dd/mm/yy",
        changeYear: true,
        showOn: "button",
    }).next('button').text('').button({
        icons: {
            primary: 'ui-icon-calendar'
        },
        label: "选择日期",
        text: false
    }).on("change", function () {
        var isreadonly = getUrlParameter('readonly');
        if (isreadonly == "y") {
            $("#mybutton").attr("disabled", "disabled")
        }
        if (isreadonly == "y") {
            $("#tb_birth").datepicker("disable");
        }
    });
});

Select allOpen in new window

I now still cannot disable the option to choose the datepicker (when readonly=y). What to adjust?

Very sorry, what is DOC READY BLOCK?

$(function() {
 // ANYTHING INSIDE HERE
})

Select allOpen in new window