Function classDirective

test/angular/1.6/angular.js:26807–26981

(name, selector)

*/

function classDirective(name, selector) {
  name = 'ngClass' + name;
  var indexWatchExpression;

  return ['$parse', function($parse) {
    return {
      restrict: 'AC',
      link: function(scope, element, attr) {
        var expression = attr[name].trim();
        var isOneTime = (expression.charAt(0) === ':') && (expression.charAt(1) === ':');

        var watchInterceptor = isOneTime ? toFlatValue : toClassString;
        var watchExpression = $parse(expression, watchInterceptor);
        var watchAction = isOneTime ? ngClassOneTimeWatchAction : ngClassWatchAction;

        var classCounts = element.data('$classCounts');
        var oldModulo = true;
        var oldClassString;

        if (!classCounts) {
          // Use createMap() to prevent class assumptions involving property
          // names in Object.prototype
          classCounts = createMap();
          element.data('$classCounts', classCounts);
        }

        if (name !== 'ngClass') {
          if (!indexWatchExpression) {
            indexWatchExpression = $parse('$index', function moduloTwo($index) {
              // eslint-disable-next-line no-bitwise
              return $index & 1;
            });
          }

          scope.$watch(indexWatchExpression, ngClassIndexWatchAction);
        }

        scope.$watch(watchExpression, watchAction, isOneTime);

        function addClasses(classString) {
          classString = digestClassCounts(split(classString), 1);
          attr.$addClass(classString);
        }

        function removeClasses(classString) {
          classString = digestClassCounts(split(classString), -1);
          attr.$removeClass(classString);
        }

        function updateClasses(oldClassString, newClassString) {
          var oldClassArray = split(oldClassString);
          var newClassArray = split(newClassString);

          var toRemoveArray = arrayDifference(oldClassArray, newClassArray);
          var toAddArray = arrayDifference(newClassArray, oldClassArray);

          var toRemoveString = digestClassCounts(toRemoveArray, -1);
          var toAddString = digestClassCounts(toAddArray, 1);