<button ng-click="login()" ng-keypress="todoSomething($event)" class="btn btn-success btn-lg" ng-disabled="loginForm.$invalid">
 登录
</button>

 $scope.todoSomething=function($event){
   if($event.keyCode==13){//回车
     login();
   }
 }

html
<button ng-click="login()" ng-enter="login()" class="btn btn-success btn-lg" ng-disabled="loginForm.$invalid">
 登录
</button>

myApp.directive('ngEnter', function () {
   return function (scope, element, attrs) {
     element.bind("keydown keypress", function (event) {
       if (event.which === 13) {
         scope.$apply(function () {
           scope.$eval(attrs.ngEnter);
         });
         event.preventDefault();
       }
     });
   };
 });