如何在javascript中将异步调用转换为同步？

Question

I am using javascript in client side and node.js in server side, Actually i have tried to make a remote validation for input fields, result must be boolean and it should be based on the server call, My code as follows,

 jQuery.validator.addMethod("remoteValidation", function(value, element) {

    var accountName = $("#accountName").val();
    var accountType = $("#accountType").val();
    var valid = this.Validation(accountType,accountName);
   //returning undefined becoz return statement executing before server side execution
    return valid;

}, "Entered email or username already exists");

 this.validation = function(accountType,accountName,cb){
    var valid =null;
  ss.rpc('AccountsManagement.userNameChecker',accountType,accountName,function(res) {
            // res will return boolean
        valid = res;
    });
            //valid is null becoz this line is executing before valid = res line.
    return valid;
};

my server side code:

   services.imAccountsService.getAllImAccounts(accountType,accountName,
   function(err,result){
    if(err){
    return;
    }
    if(result == null){
       res(true);
    }
    else{
       res(false);
    }

   });

My problem is async execution, how to make code synschronous in this situation..

Answer 1

Added function in the jquery validation method.

   if(param.type === "rpc"){
            var args = param.data.remoteArgs();
            ss.rpc(param.url, args, function(response) {
                validator.settings.messages[element.name].remote = previous.originalMessage;
                var valid = response === true;
                if ( valid ) {
                    var submitted = validator.formSubmitted;
                    validator.prepareElement(element);
                    validator.formSubmitted = submitted;
                    validator.successList.push(element);
                    validator.showErrors();
                } else {
                    var errors = {};
                    var message = response || validator.defaultMessage( element, "remote" );
                    errors[element.name] = previous.message = $.isFunction(message) ? message(value) : message;
                    validator.showErrors(errors);
                }
                previous.valid = valid;
                validator.stopRequest(element, valid);
            });
        }

It works fine ....thanks for all...

Answer 2

You will have to wait till the value of res is available. See if the below code works.

    jQuery.validator.addMethod("remoteValidation", function(value, element) {

        var accountName = $("#accountName").val();
        var accountType = $("#accountType").val();
        var valid = this.Validation(accountType,accountName);
       //returning undefined becoz return statement executing before server side execution
        return valid;

    }, "Entered email or username already exists");

     this.validation = function(accountType,accountName,cb){
        var valid =null;
      ss.rpc('AccountsManagement.userNameChecker',accountType,accountName,function(res) {
                // res will return boolean

            while(res <> null)
            {
               window.setInterval(function(){waitFunc()}, 1000);
            }
            valid = res;
        });
                //valid is null becoz this line is executing before valid = res line.
        return valid;
    };

function waitFunc()
{
//do nothing
}