@ngdoc tutorial
@name 9 - Filters
@step 9
@description

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In this step you will learn how to create your own custom display filter.

* In the previous step, the details page displayed either "true" or "false" to indicate whether
certain phone features were present or not. We have used a custom filter to convert those text
strings into glyphs: ✓ for "true", and ✘ for "false". Let's see what the filter code looks like.

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## Custom Filter

In order to create a new filter, you are going to create a `phonecatFilters` module and register
your custom filter with this module:

__`app/js/filters.js`:__

```js
angular.module('phonecatFilters', []).filter('checkmark', function() {
  return function(input) {
    return input ? '\u2713' : '\u2718';
  };
});
```

The name of our filter is "checkmark". The `input` evaluates to either `true` or `false`, and we
return one of the two unicode characters we have chosen to represent true (`\u2713` -> ✓) or false (`\u2718` -> ✘).

Now that our filter is ready, we need to register the `phonecatFilters` module as a dependency for
our main `phonecatApp` module.

__`app/js/app.js`:__

```js
...
angular.module('phonecatApp', ['ngRoute','phonecatControllers','phonecatFilters']).
...
```


## Template

Since the filter code lives in the `app/js/filters.js` file, we need to include this file in our
layout template.

__`app/index.html`:__

```html
...
 <script src="js/controllers.js"></script>
 <script src="js/filters.js"></script>
...
```

The syntax for using filters in Angular templates is as follows:

    {{ expression | filter }}

Let's employ the filter in the phone details template:



__`app/partials/phone-detail.html`:__

```html
...
    <dl>
      <dt>Infrared</dt>
      <dd>{{phone.connectivity.infrared | checkmark}}</dd>
      <dt>GPS</dt>
      <dd>{{phone.connectivity.gps | checkmark}}</dd>
    </dl>
...
```


## Test

Filters, like any other component, should be tested and these tests are very easy to write.

__`test/unit/filtersSpec.js`:__

```js
describe('filter', function() {

  beforeEach(module('phonecatFilters'));

  describe('checkmark', function() {

    it('should convert boolean values to unicode checkmark or cross',
        inject(function(checkmarkFilter) {
      expect(checkmarkFilter(true)).toBe('\u2713');
      expect(checkmarkFilter(false)).toBe('\u2718');
    }));
  });
});
```

We must call `beforeEach(module('phonecatFilters'))` before any of
our filter tests execute. This call loads our `phonecatFilters` module into the injector
for this test run.

Note that we call the helper function, `inject(function(checkmarkFilter) { ... })`, to get
access to the filter that we want to test.  See {@link angular.mock.inject angular.mock.inject()}.

Notice that the suffix 'Filter' is appended to your filter name when injected.
See the {@link guide/filter#using-filters-in-controllers-services-and-directives Filter Guide}
section where this is outlined.

You should now see the following output in the Karma tab:

<pre>Chrome 22.0: Executed 4 of 4 SUCCESS (0.034 secs / 0.012 secs)</pre>


# Experiments

* Let's experiment with some of the {@link api/ng/filter built-in Angular filters} and add the
following bindings to `index.html`:
  * `{{ "lower cap string" | uppercase }}`
  * `{{ {foo: "bar", baz: 23} | json }}`
  * `{{ 1304375948024 | date }}`
  * `{{ 1304375948024 | date:"MM/dd/yyyy @ h:mma" }}`

*  We can also create a model with an input element, and combine it with a filtered binding. Add
  the following to index.html:

  ```html
  <input ng-model="userInput"> Uppercased: {{ userInput | uppercase }}
  ```


# Summary

Now that you have learned how to write and test a custom filter, go to {@link step_10 step 10} to
learn how we can use Angular to enhance the phone details page further.


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