AngularJS ng-focus expression is evaluated when an element (window, input, select, textarea, a) gets focus.
<style>
.focusClass {background-color: yellow;}
</style>
<div ng-app="myApp" ng-controller='MyCtrl' ng-init="focus=false;">
Click on input field and click somewhere else.
<input type="text" ng-class="{focusClass: focus}" ng-focus="focus=true;" ng-blur="focus=false;"><br>
focus={{focus}}
</div>
<script src="//ajax.googleapis.com/ajax/libs/angularjs/1.5.3/angular.min.js"></script>
<script>
var module = angular.module('myApp', []);
module.controller('MyCtrl', function($scope) {});
</script>
