php - $.ajax.done works on Firefox but not in Chrome -

i have simple ajax request jquery , php. code

var request = $.ajax({     method: "post",     url: "url.php",     data: { param: valueparam },     datatype: "html" });  request.done(function(html) {    alert('hello'); }); 

the code works perfect in firefox 38.0.5 not works in chrome 43.0.2357.124m.

the problem in chrome follow: "url.php" returns pair name-value. if returns value distinct null, alert not displayed (and there isn't error in console). if url return null value, alert displayed. tried ctrl+f5 not works.

in firefox works in both cases.

thanks!

does fail function return something?

request.done(function( msg ) {   console.log(msg); });  request.fail(function( jqxhr, textstatus ) {   console.log("request failed: "+textstatus); });