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Filters are just functions which transform input to an output. However filters need to be Dependency Injected. To achieve this a filter definition consists of a factory function which is annotated with dependencies and is responsible for creating a filter function.

    // Filter registration
    function MyModule($provide, $filterProvider) {
      // create a service to demonstrate injection (not always needed)
      $provide.value('greet', function(name){
        return 'Hello ' + name + '!';
      });

      // register a filter factory which uses the
      // greet service to demonstrate DI.
      $filterProvider.register('greet', function(greet){
        // return the filter function which uses the greet service
        // to generate salutation
        return function(text) {
          // filters need to be forgiving so check input validity
          return text && greet(text) || text;
        };
      });
    }

The filter function is registered with the `$injector` under the filter name suffix with `Filter`.

    it('should be the same instance', inject(
      function($filterProvider) {
        $filterProvider.register('reverse', function(){
          return ...;
        });
      },
      function($filter, reverseFilter) {
        expect($filter('reverse')).toBe(reverseFilter);
      });

For more information about how angular filters work, and how to create your own filters, see Filters in the Angular Developer Guide.

## Methods

- ###

  `register(name);`

  #### Parameters

  Param | Type | Details
  --- | --- | ---
  name | string Object | Name of the filter function, or an object map of filters where the keys are the filter names and the values are the filter factories.

  #### Returns

  Object | Registered filter instance, or if a map of filters was provided then a map of the registered filter instances.