更新：
ngKeypress，
ngKeydown而
ngKeyup现在AngularJS的一部分。
<!-- you can, for example, specify an expression to evaluate --><input ng-keypress="count = count + 1" ng-init="count=0"><!-- or call a controller/directive method and pass $event as parameter. With access to $event you can now do stuff like finding which key was pressed --><input ng-keypress="changed($event)">
在这里阅读更多：
https://docs.angularjs.org/api/ng/directive/ngKeypress
https://docs.angularjs.org/api/ng/directive/ngKeydown
https://docs.angularjs.org/api/ng/directive/
ngKeyup
较早的解决方案：
解决方案1：
ng-change与
ng-model
<input type="text" placeholder="+639178983214" ng-model="mobileNumber" ng-controller="RegisterDataController" ng-change="keydown()">
JS：
function RegisterDataController($scope) { $scope.keydown = function() { };}解决方案2.使用
$watch
<input type="text" placeholder="+639178983214" ng-model="mobileNumber" ng-controller="RegisterDataController">
JS：
$scope.$watch("mobileNumber", function(newValue, oldValue) { });
