# Grouped Queue

In memory queue system prioritizing tasks.

# Documentation

## Installation

```bash
npm install --save grouped-queue
```

## Methods

### Constructor

The constructor takes an optional array of task groups. The first `String` name will be the first queue to be emptied, the second string will be the second group emptied, etc.

By default, the constructor will always add a `default` queue in the last position. You can overwrite the position of the `default` group if you specify it explicitly.

```javascript
import Queue from "grouped-queue";

const queue = new Queue(["first", "second", "third"]);
```

### Queue#add `add( [group], task, [options] )`

Add a task into a group queue. If no group name is specified, `default` will be used.

Implicitly, each time you add a task, the queue will start emptying (if not already running).

Each task function is passed a callback function. This callback must be called when the task is complete.

```javascript
queue.add((cb) => {
  DB.fetch().then(cb);
});
```

#### Option: `once`

You can register tasks in queues that will be dropped if they're already planned. This is done with the `once` option. You pass a String (basically a name) to the `once` option.

```javascript
// This one will eventually run
queue.add(method, { once: "readDB" });

// This one will be dropped as `method` is currently in the queue
queue.add(method3, { once: "readDB" });
```

#### Option: `run`

You can register a task without launching the run loop by passing the argument `run: false`.

```javascript
queue.add(method, { run: false });
```

### Delaying runs

If you don't want tasks to run as they're added, you can hold the queue until manually starting.

```javascript
const queue = new Queue(
  ["first", "second", "third"],
  // `runOnAdd` option; this boolean instruct the queue to not auto-start.
  false,
);

// Later on, to start processing
queue.start();

// And pause to stop processing new tasks; running task will complete.
queue.pause();
```

## Events

### `end`

This event is called **each time** the queue emptied itself.

```javascript
queue.on("end", () => {
  console.log("done!");
});
```

# Contributing

- **Unit test**: Unit tests are written in Mocha. Please add a unit test for every new feature
  or bug fix. `npm test` to run the test suite.
- **Documentation**: Add documentation for every API change. Feel free to send corrections
  or better docs!
- **Pull Requests**: Send _fixes_ PR on the `master` branch.

# License

Copyright (c) 2013 Simon Boudrias (twitter: @vaxilart)  
Licensed under the MIT license.