@ngdoc overview
@name Developer Guide: Templates: Filters: Creating Angular Filters
@description

Writing your own filter is very easy: just define a JavaScript function on the `angular.module.ng.$filter`
object.
The framework passes in the input value as the first argument to your function. Any filter
arguments are passed in as additional function arguments.

You can use these variables in the function:

* `this` — The current scope.
* `this.$element` — The DOM element containing the binding. The `$element` variable allows the
filter to manipulate the DOM.

The following sample filter reverses a text string. In addition, it conditionally makes the
text upper-case and assigns color.

<doc:example module="MyReverseModule">
<doc:source>
<script type="text/javascript">
  angular.module('MyReverseModule', []).
    filter('reverse', function() {
      return function(input, uppercase) {
        var out = "";
        for (var i = 0; i < input.length; i++) {
          out = input.charAt(i) + out;
        }
        // conditional based on optional argument
        if (uppercase) {
          out = out.toUpperCase();
        }
        return out;
      }
    });

  function Ctrl($scope) {
    $scope.greeting = 'hello';
  }
</script>

<div ng:controller="Ctrl">
  <input ng:model="greeting" type="greeting"><br>
  No filter: {{greeting}}<br>
  Reverse: {{greeting|reverse}}<br>
  Reverse + uppercase: {{greeting|reverse:true}}<br>
</div>
</doc:source>
<doc:scenario>
  it('should reverse greeting', function() {
    expect(binding('greeting|reverse')).toEqual('olleh');
    input('greeting').enter('ABC');
    expect(binding('greeting|reverse')).toEqual('CBA');
  });
</doc:scenario>
</doc:example>


## Related Topics

* {@link dev_guide.templates.filters Understanding Angular Filters}
* {@link dev_guide.compiler Angular HTML Compiler}

## Related API

* {@link api/angular.module.ng.$filter Angular Filter API}
