# React Graceful Image

An image component for gracefully dealing with image errors, by providing optional lazy loading, optional placeholder and configurable retries on failure. Particularly useful in situations where your application might be used in poor signal areas such as when travelling on a train, a bus or a car.

### Example

<table>
<tr>
<th>1</th>
<th>2</th>
<th>3</th>
<th>4</th>
</tr>
  <tr>
    <td><img src='https://user-images.githubusercontent.com/16339741/35174790-8ebe4bcc-fd68-11e7-935b-f15407ef2d94.png' alt='browser broken image' width='200' height='129.411764706'></td>
    <td><img src='https://user-images.githubusercontent.com/16339741/35175624-6aad9568-fd6c-11e7-9aa0-329a5d2b1728.png' alt='browser with placeholder image' width='200' height='129.411764706'></td>
    <td><img src='https://user-images.githubusercontent.com/16339741/35175639-83d1a656-fd6c-11e7-9812-480c251acf98.png' alt='browser without placeholder image' width='200' height='129.411764706'></td>
    <td><img src='https://user-images.githubusercontent.com/16339741/35177052-c962542e-fd74-11e7-8b46-325f444c7970.png' alt='browser with working image after retry' width='200' height='129.411764706'></td>
  </tr>
</table>

1. Default browser behaviour when image fails due to bad signal
2. With react-graceful-image placeholder
3. With react-graceful-image disabled placeholder
4. With react-graceful-image retries - if the image fails to load, the package will gracefully re-attempt loading the image again

_(***note:*** these are not mutually exclusive, for example the default behaviour makes use of both 2 & 4 together.)_

### Installation

```sh
npm install --save react-graceful-image
```

### Basic Usage

```js
<Image
    src='path_to_image'
    width='300'
    height='300'
    alt='My awesome image'
/>
```

### Default Behaviour

1. Render an SVG placeholder - if environment doesn't support SVG, then avoid rendering the placeholder
2. Check if placeholder is within the visible viewport - if so then load the image
3. If image loads successfully - display the image by fading it in
4. If image fails to load - retry loading the image starting with a 2 second delay and doubling it with every retry _(by default retry stops after 8 tries)_

### Prop Options

| Prop                   | Description                                                                      | Default                                          | Type     |
| ---------------------- | -------------------------------------------------------------------------------- | ------------------------------------------------ | -------- |
| **`Any valid html image prop`**   | Any valid html image prop | _none_  | _valid html image prop_   |
| **`placeholderColor`** | Placeholder's color                                                              | _`'#eee'`_                                       | _string_ |
| **`noPlaceholder`**    | Turn off placeholder rendering                                                   | _false_                                          | _bool_   |
| **`customPlaceholder`**    | Provide a custom placeholder. This should be a function taking a ref and setting it on your custom placeholder so that its position could be observed within the viewport | _null_ | _Function returning a component_   |
| **`retry`**            | Retry algorithm's configuration, consisting of `count`, `delay` and `accumulate` | _`{count: 8, delay: 2, accumulate: 'multiply'}`_ | _object_ |
| **`onLoad`**            | Callback that will be invoked when an image loads | _none_ | _function_ |
| **`onError`**            | Callback that will be invoked after the retry algorithm has finished and the image still hasn't been loaded | _none_ | _function_ |
| **`noLazyLoad`**       | Turn off lazy loading   | _false_    | _bool_   |

### Retry

You can modify the default retry algorithm by supplying a `retry` prop consisting of 3 properties: `count`, `delay` and `accumulate`:

- `count` specifies the number of times you want to retry
- `delay` specifies the delay between retries (in seconds)
- `accumulate` specifies how the delay should increase with each retry, **_possible values:_** `'multiply'` (default), `'add'` or `false` (false can also be represented by simply omitting this property)

#### Accumulate

- `accumulate: 'multiply'` will multiply delay after each retry by the given `delay` value, i.e. if `delay: 2` is given then 1st retry will be in 2 seconds, 2nd retry will be in 4 seconds, 3rd retry will be in 8 seconds, 4th retry will be in 16 seconds etc.
- `accumulate: 'add'` will increment delay after each retry by the given `delay` value, i.e. if `delay: 2` is given then 1st retry will be in 2 seconds, 2nd retry will be in 4 seconds, 3rd retry will be in 6 seconds, 4th retry will be in 8 seconds, etc.
- `accumulate: 'false'` will keep the delay constant between retries, i.e. if `delay: 2` is given then retry will run every 2 seconds

### Examples

**1**: The below code snippet will display a grey placeholder until the user scrolls it into view at which point it will be lazily swapped in for the real image. If, however, the real image fails to load, then the retry algorithm is going to kick in and try loading the image again for a maximum of 8 times, with an initial delay of 2 seconds, which will then increase to 4 seconds, then to 8 seconds, then to 16 seconds, and so on (default retry configuration).

```js
<Image
    src='path_to_image'
    className='content-image'
    alt='My awesome image'
    onLoad={ onLoadCallback }
    onError={ onErrorCallback }
/>
```

**2**: The below code snippet will display a grey placeholder until the user scrolls it into view at which point it will be lazily swapped in for the real image. If, however, the real image fails to load, then the retry algorithm is going to kick in and try loading the image again for a maximum of 10 times, with a fixed 2 second delay in-between each retry.


```js
<Image
    src='path_to_image'
    width='250'
    height='250'
    style={{ padding: '20px' }}
    alt='My awesome image'
    retry={{ count: 10, delay: 2 }}
    onLoad={ onLoadCallback }
    onError={ onErrorCallback }
/>
```

**3**: The below code snippet will display, a custom, your own provided placeholder until the user scrolls it into view at which point it will be lazily swapped in for the real image. If, however, the real image fails to load, then the retry algorithm is going to kick in and try loading the image again for a maximum of 15 times, with initial delay of 3 seconds which will then increase to 6 seconds, then to 9 seconds, then to 12 seconds, and so on.

```js
<Image
    src='path_to_image'
    width='150'
    height='150'
    style={{ padding: '20px' }}
    alt='My awesome image'
    customPlaceholder={ ref => <SomePlaceholder refProp={ ref } /> }
    retry={{ count: 15, delay: 3, accumulate: 'add' }}
    onLoad={ onLoadCallback }
    onError={ onErrorCallback }
/>
```