manipulating slider with jquery

i have this very basic slider

      "width_id" ng-model="width" min="20" step="1" max="320">                          

i want to check every 4 seconds the value from other element whose class is yyyy and i can say that it is giving desired result when i run in console

setInterval(function() {
var testtyyyuy =$(".yyyy").outerWidth()+60;

//$("#width_id").value(testtyyyuy);
$("#width_id").attr("aria-valuenow", testtyyyuy).css("width", testtyyyuy);
}, 40000);

gives error

   VM64:1 Uncaught TypeError: Cannot read property 'attr' of null

i have tried aria-valuenow because after the html is loaded it adds the value of slider in aria-valuenow

but when i run that code i get error

i tried slider also

$("#width_id").slider('value',300);

but it gives error

 VM60:1 Uncaught TypeError: Cannot read property 'slider' of null

any help is getting this will be helpful i get the correct data from var testtyyyuy and it has been verified in console