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# Interchange

JavaScript

Interchange uses media queries to dynamically load responsive content that is appropriate for the user's device.

## Use with Images

Bandwidth is precious on mobile networks, so it helps to serve users on smaller screens a smaller image. Using Interchange, you can serve up specific images for users depending on their screen size. CSS media queries are used to determine what size the user's device is, and which image should be served.

In the above example, we have three different sizes of image: one for small screens, one for medium, and one for large. Use the below format to set up a responsive image. The image will change automatically as the browser resizes.

    <img data-interchange="[assets/img/interchange/small.jpg, small], [assets/img/interchange/medium.jpg, medium], [assets/img/interchange/large.jpg, large]">

The image set is a comma-separated list of items with this format:

    [image_path, media_query]

`image_path` can be a relative or absolute path. `media_query` can be any CSS media query, or a Foundation breakpoint—see Named Media Queries below.

Interchange evaluates rules in order, and the last rule to match will be used. For this reason, you should order your rules from smallest screen to largest screen.

## Use with HTML

Interchange can also swap in and out entire chunks of HTML. This allows you to load in mobile-friendly components on small screens, or more advanced versions on large screens.

In the below example, we've applied `data-interchange` to a `<div>` instead of an `<img>` element, and the paths are to HTML files instead of images.

    <div data-interchange="[assets/partials/interchange-default.html, small], [assets/partials/interchange-medium.html, medium], [assets/partials/interchange-large.html, large]"></div>

## Use with Background Images

When using Interchange on a non-`<img>` element, you can pass in an image path instead of an HTML path, and the element's `background-image` property will be set to the path of the matching rule.

    <div data-interchange="[assets/img/interchange/small.jpg, small], [assets/img/interchange/medium.jpg, medium], [assets/img/interchange/large.jpg, large]"></div>

## Named Media Queries

Interchange supports named queries as shorthands for full CSS media queries. Any breakpoint defined in the `$breakpoints` variable in your Sass will work, along with a few other keywords. Learn more about changing the default breakpoints.

Query Name | Media Query
--- | ---
small | `screen and (min-width: 0em)`
medium | `only screen and (min-width: 40em)`
large | `only screen and (min-width: 64em)`
xlarge | `only screen and (min-width: 75em)`
xxlarge | `only screen and (min-width: 90em)`
portrait | `screen and (orientation: portrait)`
landscape | `screen and (orientation: landscape)`
retina | `only screen and (-webkit-min-device-pixel-ratio: 2), only screen and (min--moz-device-pixel-ratio: 2), only screen and (-o-min-device-pixel-ratio: 2/1), only screen and (min-device-pixel-ratio: 2), only screen and (min-resolution: 192dpi), only screen and (min-resolution: 2dppx)`

To add your own named media queries, add them as properties to `Foundation.Interchange.SPECIAL_QUERIES`.

    Foundation.Interchange.SPECIAL_QUERIES['square'] = 'screen and (aspect-ratio: 1/1)';

## Programmatic Use

When using Interchange programmatically, you need to pass in your ruleset in the `options` object, as well as the container element, not the content elements, like so:

    var $photoFrame = $('#some-container');
    var interchange = new Foundation.Interchange($photoFrame, {
      rules: [
        "[path/to/default.jpg, small]",
        "[path/to/medium.jpg, medium]",
        "[path/to/large.jpg, large]"
      ]
     });

## JavaScript Reference

### Initializing

The file `foundation.interchange.js` must be included in your JavaScript to use this plugin, along with `foundation.core.js`. This plugin also requires these utility libraries:

- `foundation.util.mediaQuery.js`

- `foundation.util.timerAndImageLoader.js`

### Foundation.Interchange

Creates a new instance of Interchange.

    var elem = new Foundation.Interchange(element, options);

Fires these events: Interchange#event:init

Name | Type | Description
--- | --- | ---
`element` | Object | jQuery object to add the trigger to.
`options` | Object | Overrides to the default plugin settings.

### Plugin Options

Use these options to customize an instance of Interchange. Plugin options can be set as individual data attributes, one combined `data-options` attribute, or as an object passed to the plugin's constructor. Learn more about how JavaScript plugins are initialized.

Name | Type | Default | Description
--- | --- | --- | ---
`data-rules` | `array` | `null` | Rules to be applied to Interchange elements. Set with the `data-interchange` array notation.

### Events

These events will fire from any element with a Interchange plugin attached.

Name | Description
--- | ---
`replaced.zf.interchange` | Fires when content in an Interchange element is done being loaded.

### Methods

#### replace

    $('#element').foundation('replace', path);

Update the `src` property of an image, or change the HTML of a container, to the specified path.

Fires these events: Interchange#event:replaced

Name | Type | Description
--- | --- | ---
`path` | String | Path to the image or HTML partial.

#### destroy

    $('#element').foundation('destroy');

Destroys an instance of interchange.