I have used this function for username availability check :

function ShowAvailability() {
$.ajax({
type: “POST”,
url: “CS.aspx/CheckUserName”,
data: ‘{userName: “‘ + $(“#”)[0].value + ‘” }’,
contentType: “application/json; charset=utf-8″,
dataType: “json”,
success: OnSuccess,
failure: function(response) {
alert(response);
}
});
}

what if I removed dataType: “json” from this $.ajax method . then what happened?

I have read article in which its written that :

You see, in an Ajax environment where we make calls to web services we expect to get some data back in some form. Well, if we receive XML back as a direct result of an Ajax call, we have to send that data through an XML parser before we can even begin to manipulate the data to be useful to JavaScript. If we receive the data in JSON…we don’t have to do anything but assign the results to a variable because JSON is already JavaScript. From there, we can manipulate the data as normal.

can u provide me example by providing simple code which will illustrate above statement ?

input type=”hidden” id=”json_data_island” value=”{prop:’value’, prop2:['value1','value2','value3']}”

And then

var the_data = eval(‘(‘ + document.getElementById(‘json_data_island’).value + ‘)’);
alert(the_data.prop2);

No problems with ie5/5.5, gecko white spaces etc.

Not exactly in this case. It would contain only content, as well as HTML.

Also, Internet Explorer 5 & 5.5 don’t add comment nodes to the DOM so the script will fail in those browser versions.

Personally, I like the idea but prefer to get my server-side code to add the appropriate javascript to the head of the document (when possible).