How can I detect keydown or keypress event in angular.js?

Update:

ngKeypress, ngKeydown and ngKeyup are now part of AngularJS.

<!-- 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)">

Read more here:

https://docs.angularjs.org/api/ng/directive/ngKeypress
https://docs.angularjs.org/api/ng/directive/ngKeydown
https://docs.angularjs.org/api/ng/directive/ngKeyup

Earlier solutions:

Solution 1: Use ng-change with ng-model

<input type="text" placeholder="+639178983214" ng-model="mobileNumber" 
ng-controller="RegisterDataController" ng-change="keydown()">

JS:

function RegisterDataController($scope) {       
   $scope.keydown = function() {
        /* validate $scope.mobileNumber here*/
   };
}

Solution 2. Use $watch

<input type="text" placeholder="+639178983214" ng-model="mobileNumber" 
ng-controller="RegisterDataController">
    

JS:

$scope.$watch("mobileNumber", function(newValue, oldValue) {
    /* change noticed */
});