jQuery validator and a custom rule that uses AJAX

For anyone else who stumbles upon this, validate supports 'remote' method, which may not have existed in 2010:

https://jqueryvalidation.org/remote-method/

$("#myform").validate({  rules: {    email: {      required: true,      email: true,      remote: {        url: "check-email.php",        type: "post",        data: {          username: function() {            return $("#username").val();          }        }      }    }  }});

You are doing an AJAX request, ergo: the validation is already finished working when your custom validator returns either true or false.

You will need to work with async. See also this post: How can I get jQuery to perform a synchronous, rather than asynchronous, Ajax request?

Something like:

function myValidator() {   var isSuccess = false;   $.ajax({ url: "",             data: {},             async: false,             success:                 function(msg) { isSuccess = msg === "true" ? true : false }          });    return isSuccess;}

Warning:

As of jQuery 1.8, the use of async: false with jqXHR ($.Deferred) is deprecated; you must use the success/error/complete callback options instead of the corresponding methods of the jqXHR object such as jqXHR.done() or the deprecated jqXHR.success().

It took me forever to figure out how to get a jsonified string containing the value of an element in the page into the remote request- this is the result of a combination of many hours and trying many search results.

Key points:

1. async:false has been deprecated,

2. the function call right after remote: is the key for creating the data string with the element's value. Trying to access a current value from the form after data: was returning a blank value for the field with dataType set as json.

       $("#EmailAddress").rules("add", {    required: true,    remote: function () { // the function allows the creation of the data string                           // outside of the remote call itself, which would not                           // return a current value from the form.        var emailData = "{'address':'" +                         $('#SignupForm :input[id$="EmailAddress"]').val() +                         "'}";        var r = {            url: "foobar.aspx/IsEmailAvailable",            type: "post",            dataType: "json",            contentType: "application/json; charset=utf-8",            cache: false,            data: emailData,            dataFilter: function(response) {                this.email_run = true; //fix for race condition with next button                return isAvailable(data); //return true or false            }        };        return r;    },    messages: {        remote: "* Email in use"    }});

.ASPX page:

<input id="EmailAddress" required name="Email" type="email" placeholder="Email Address*" runat="server"/>

C# Code Behind:

[WebMethod]    public static object IsEmailAvailable(string address){...}

Formatting the response object:

function isAvailable(data) {    var response = JSON.parse(getJsonObject(data));    return (response.isAvailable === "True") ? true : false;};//transform response string to a JavaScript Object()//http://encosia.com/never-worry-about-asp-net-ajaxs-d-again/ function getJsonObject(data) {    var msg = eval('(' + data + ')');    if (msg.hasOwnProperty('d'))        return msg.d;    else        return msg;};