AngularJS 1.5.x

var app = angular.module('plunker', []);

app.controller('MainCtrl', function() {
  var ctrl = this;
  
  ctrl.keydown = function(e){
    ctrl.capsLockOn = e.getModifierState( 'CapsLock' );
  }
  
});

<!DOCTYPE html>
<html ng-app="plunker">

  <head>
    <meta charset="utf-8" />
    <title>AngularJS Plunker</title>
    <script>document.write('<base href="' + document.location + '" />');</script>
    <link rel="stylesheet" href="style.css" />
    <script data-require="angular.js@1.5.x" src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.11/angular.min.js" data-semver="1.5.11"></script>
    <script src="app.js"></script>
  </head>

  <body ng-controller="MainCtrl as vm">
    <input ng-model="name" ng-keydown="vm.keydown($event)" />
    <p>Is capslock on? {{vm.capsLockOn}}</p>
  </body>

</html>

/* Put your css in here */