What property? If it's a server-side property, then you're going to have
some work ahead of you.

Where do you want to do this? On an .aspx page?

Are you talking about making a field on a list form readonly?

yes,
i want to make a field readonly..

I use the SmartTools jQuery for SharePoint solution available here to
make jQuery available to me:

http://smarttools.codeplex.com/
<http://smarttools.codeplex.com/wikipage?title=jQuery&referringTitle=Hom
e>

And then on the edit form that I want to have read only fields I add a
Content Editor Web Part with the following code in it. Rather than set
the field to "readonly" this will make the field non-editable. I have
found that if I set  a field to readonly, the value in the field is
blanked out when the form is submitted back and thus you lose the very
value you were trying to lock down

<script language="javascript" type="text/javascript">

// Determines if the web part page is in design mode

// by looking at hidden fields produced by SharePoint

function IsInDesignMode()

{

if(document.getElementById("MSOLayout_InDesignMode").value == '1')
return true;

if(document.getElementById("MSOTlPn_SelectedWpId").value != "")
return true;

return false;

}



function kickStart() {

$(":input[title='Batch Status']").attr('disabled', true);

$(":input[title='Report Type']").attr('disabled', true);

}



if (IsInDesignMode() != true) {

_spBodyOnLoadFunctionNames.push("kickStart");

}



</script>

I'm interested in what I consider to be extraneous code...

I would have considered only to use:

<script type="text/javascript" src="jQuery.js" />
<script type="text/javascript">

$(document).ready(function() {
$("input[title='Batch Status']").attr('disabled', true);
});

</script>

In answer to your questions:
Your solution does pare the code required down to the very bare minimum.

If you use the SmartTools solution, the jQuery library is loaded on
every page and yes it would be cached. I use jQuery all over the place
so it's easier for me to do it that way.

I use that custom IsInDesignMode() function in combination with the
_spBodyOnLoadFunctionNames.push("kickStart");

instead of just $(document).ready(function() {}

because it allows to me to go into design mode on a page and not have
the custom javascript code running.

That is definitely an obnoxious aspect of going into Edit
Mode...I will look more deeply into this idea. We are already determining the
usefulness of using the SmartTools because we need to centralize our jQuery
hosting for our Farms. This may add a boost to its need (O;

consider this project as well:
http://spcs.codeplex.com/