# core/queue/worker/merge

This module provides a class to organize a [[WorkerQueue]] data structure with support of task merging by a specified hash function.
It means that the same tasks aren't duplicated. See [`core/queue/worker`](src_core_queue_worker.html) and
[`core/queue`](src_core_queue.html) for more information.

## Usage

```js
import MergeQueue from 'core/queue/worker/merge';

const queue = new MergeQueue((task) => {
  console.log(task);
}, {
  concurrency: 2,
  refreshInterval: 50,
  hashFn: (task) => JSON.stringify(task)
});

queue.push({a: 1});
queue.push({a: 1});

console.log(queue.length); // 0

queue.push({a: 2});

console.log(queue.length); // 0

queue.push({a: 3});

console.log(queue.length); // 1

queue.push({a: 4});

console.log(queue.length); // 2

queue.clear();
console.log(queue.length); // 0
```

### Providing a hash function

To provide a function to calculate task hashes, use the structure constructor `hashFn` option.
By default, all hashes are calculated via `Object.fastHash`.

```js
import MergeQueue from 'core/queue/worker/merge';

const queue = new MergeQueue((task) => {
  console.log(task);
}, {
  hashFn: (task) => JSON.stringify(task)
});

queue.push({a: 1});
queue.push({a: 1});
```