Alphabets only directive

I am trying to achieve a directive that would be used to accept only alphabets into the text box i.e from a-z or A-z I did try to do this by,

 angular.module('myApp', []).directive('alphabetsOnly', function(){
return {
 require: 'ngModel',
 link: function(scope, element, attrs, modelCtrl) {
   modelCtrl.$parsers.push(function (inputValue) {

       if (inputValue == undefined) return '' 
       var transformedInput = inputValue.replace(/^[a-zA-Z]+$/, ''); 
       if (transformedInput!=inputValue) {
          modelCtrl.$setViewValue(transformedInput);
          modelCtrl.$render();
       }         

       return transformedInput;         
   });
 }
};
});

function MyCtrl($scope) {
$scope.name = ''
}

but this does not works .

tried with pattern

'/^[a-zA-Z]$/' 

but no success. Can anyone help me with this.