javascript - Missing parameter in Ajax post to Asmx -

i'm trying send string file asmx service , keep getting following error:

    message: invalid web service call, missing value parameter: file     stacktrace    @ system.web.script.services.webservicemethoddata.callmethod(object target, idictionary`2 parameters) @  system.web.script.services.webservicemethoddata.callmethodfromrawparams(object target, idictionary`2 parameters)\\r\\n   @  system.web.script.services.resthandler.invokemethod(httpcontext context, webservicemethoddata methoddata, idictionary`2 rawparams)\\r\\n   @  system.web.script.services.resthandler.executewebservicecall(httpcontext context, webservicemethoddata methoddata)\",\"exceptiontype\":\"system.invalidoperationexception\"} 

here's js

function ajaxactionpostdata(service, operation, file, callback, async) {     if (!async) { async = false; }     $.ajax({         type: 'post',         url: '/api/service.asmx/operation',         contenttype: 'application/json; charset=utf-8',         async: async,         data: "{ 'file': '" + file + "' }",         datatype: 'json',         success: function (msg) { if (msg) { callback(msg.d); } },         error: errorhandler     }); } 

when passed function above file has value of "test\r\n" escape characters messing it?

service code

    [webmethod(enablesession = true)]     [scriptmethod(responseformat = responseformat.json)]     public bool uploadcsv(string id, string file)     {         string testfile = file;         return true;     } 

no other errors thrown, file not having value. i've tried various things cannot understand i'm missing?

try sending data plain object:

data: { 'file': file }, 

or string:

data: 'file=' + file, 

at moment you're doing little of both won't work.