## Asynchronous Runtime Balancer

> The async processing model is automatically observed by a runtime balancer to prevent any blocking issues, even on page load.

Those methods of each index type provides an async version:

- addAsync()
- appendAsync()
- updateAsync()
- removeAsync()
- searchAsync()

All those async versions always return a `Promise`, although a callback can be passed additionally as the <u>last parameter</u>.

When calling async methods of the index, a runtime balancer observe the current event loop and will pass to the next event loop automatically.

### Task Priority

You can control how early the process should move over to the next event loop by passing the option property `priority`:

```js
const index = new Index({
    // a value between 1 and 9
    priority: 4
});
```

The lowest valid priority number is `1` and is typically known as `idle` (event loop cycles by native ~4ms). The default priority is `4` which is optimized for non-blocking user interfaces within a browser (event loop cycles every ~45ms).
When you have some very smooth running animation you should use a priority of `2` to keep the animation running by 60 fps without any stutter. Targeting 120 fps or higher you should use `1`.

On Node.js you can slightly increase this priority e.g. to `6`, because here there is no UI involved. 
A priority value of `9` will cycle the event loop on every ~250ms which is the maximum recommended blocking time. You should not use a value higher than this.

### Polling Tasks

Do not forget to `await` on <u>every</u> async task you apply to the index:

```js
for(let i = 0; i < 99999999; i++){
    await index.addAsync(i, "test " + i);
}
```

You can perform queries to the index during any other async batch is running.

### Examples

You can assign callbacks to each async function:

```js
index.addAsync(id, content, function(){
    console.log("Task Done");
});

index.searchAsync(query, function(result){
    console.log("Results: ", result);
});
```

Or do not pass a callback function and getting back a `Promise` instead:

```js
index.addAsync(id, content).then(function(){
    console.log("Task Done");
});

index.searchAsync(query).then(function(result){
    console.log("Results: ", result);
});
```

Or use `async` and `await`:

```js
async function add(){
    await index.addAsync(id, content);
    console.log("Task Done");
}

async function search(){
    const results = await index.searchAsync(query);
    console.log("Results: ", result);
}
```