Adding nunjucks filters and functions

Adding Functions for All Templates

Apostrophe provides a number of handy functions like aposArea that can be called from any Nunjucks template. Sometimes you'll want to add your own.

You can do that with the apos.addLocal method, which is easy to call from afterInit in your app.js file, like so:

    afterInit: function(callback) {
      site.apos.addLocal('doubleIt', function(a) {
        return a * a;
      });
      return callback(null);
    }

Now you can call doubleIt in a template:

    Two times four is {{ doubleIt(4) }}.

Notice that locals do not take a callback. If you need to do something asynchronous you must do it before the rendering of the page begins. Check out page loader functions for more information.

Adding Filters for Nunjucks

Here's a simple example of a Nunjucks filter at work in a page template:

```markup
<h1>{{ page.title | e }}</h1>
```

The e filter escapes plaintext as HTML. Apostrophe provides several more really handy nunjucks filters, but it doesn't cover everything. Sometimes you'll want to add your own filters.

To add your own filters, provide a configureNunjucks function in app.js. Here you can manipulate each Nunjucks environment before it is used. Here's an example:

    configureNunjucks: function(env) {
      env.addFilter('repeat', function(s, n) {
        var r = '';
        while (n--) {
          r += s;
        }
        return r;
      });
    }

Now we can repeat something any number of times in Nunjucks templates anywhere in our Apostrophe project:

    {{ page.title | repeat(3) }}

Asynchronous filters are not supported. Use page loader functions to fetch data before your page templates start rendering.