jquery - JavaScript setTimeout() delay -

i encountering problem delay of window.settimeout() seems ignored or randomized.

function timer() {     var refreshtimer = 0;      var delay = 300000; // 5 min      this.init = function () {         this.startrefreshtimer();         $(document)             .ajaxstop(this.startrefreshtimer)             .ajaxstart(this.stoprefreshtimer)         ;     };      this.startrefreshtimer = function() {         refreshtimer = window.settimeout(resettimer, delay - 10000);     };      this.stoprefreshtimer = function() {         window.cleartimeout(refreshtimer);     };      function resettimer() {         $.ajax(url);     }      this.init(); } 

this works random set of times (and in multiple browsers , tabs) after while delay breaks out.

here's log of request times:

17:50:04 17:54:55 // + 5 min - ~10 sec 17:59:46 // || 18:04:37 // || 18:09:28 // || 18:14:19 // || 18:19:10 // || 18:24:01 // || 18:28:52 // || 18:33:43 // || 18:38:34 // || 18:43:25 // || 18:48:16 // || 18:53:07 // || 18:57:58 // || 19:15:09 // + ~ 17 min ??? 

i cannot use window.setinterval() , not give more information purspose of code. want know if has made similar experiences and/or knows of solution problem.