ngModel

https://docs.angularjs.org/error/ngModel/numfmt?p0=sa

angular.module('myApp', [])

.directive('tagList', [function () {
  return {
    require: 'ngModel',
    link: function (scope, elem, attrs, ngModel) {
      var toView = function (val) {
        return (val || []).join(', ');
      };

      var toModel = function (val) {
        return (val || '').split(',').map(function (v) {
          return v.trim();
        });
      };

      ngModel.$formatters.unshift(toView);
      ngModel.$parsers.unshift(toModel);
    }
  };
}]);