# addExtra(key, extra)

### **Arguments**

1. `key` *(string)*: Key to store the extra under (represents given item).
2. `extra` *(object)*: Extra data to store.

### **Throws**

1. If `extra` is not an object, it will throw `'extra' must be an object.`

### **Lifecycle**

1. **preAddExtra**

   **Event name:** `preAddExtra`\
   **Properties passed:**

   * `cacheInstance` reference to cache instance (`this`)
   * `key` key passed to `addExtra` method
   * `extra` extra passed to `addExtra` method

   **Returns:** *(object)*: object containing properties:

   * `cacheInstance` reference to cache instance (`this`)
   * `key` key passed through handlers added for `preAddExtra` event
   * `extra` extra passed through handlers added for `preAddExtra` event<br>
2. **postAddExtra**

   **Event name:** `postAddExtra`\
   **Properties passed:**

   * `cacheInstance` reference to cache instance (`this`) returned by `preAddExtra`
   * `key` key returned by `preAddExtra`
   * `extra` extra (object) returned by adapter using its [addExtra](https://stash-it.gitbook.io/stash-it/api/adapter/addextra-key-extra) method

   **Returns:** *(object)*: object containing properties:

   * `cacheInstance` reference to cache instance (`this`)
   * `key` key passed through handlers added for `postAddExtra` event
   * `extra` extra passed through handlers added for `postAddExtra` event<br>

   Eventually `addExtra` returns extra returned by `postAddExtra`.

### **Example**

```javascript
// Existing extra in an item
{ 
    some: 'data'
}

cache.addExtra(key, { foo: 'bar' });

// Extra after adding new one
{
    foo: 'bar',
    some: 'data'
}

cache.addExtra(key, { foo: 'baz' });

// Extra after another round of adding stuff to it
{
    foo: 'baz', // <-- notice that this value's changed
    some: 'data'
}
```