документацию читай
https://docs.angularjs.org/api/ng/service/$interval
https://docs.angularjs.org/api/ng/service/$timeout
angular
.module('App', [])
.controller('MainCtrl', ['$scope', '$interval', function($scope, $interval){
$interval(function(){
var x = Math.random();
$scope.a = x;
},1000);
}]);