## Usage

```js
const Base = require('base');
const tasks = require('base-task');

const base = new Base();
base.use(tasks());

/**
 * Define tasks
 */

base.task('foo', function(cb) {
  console.log('this is foo!');
  cb();
});
base.task('bar', function(cb) {
  console.log('this is bar!');
  cb();
});

/**
 * Build tasks
 */

base.build(['foo', 'bar'])
  .then(() => {
    // this is foo!
    // this is bar!
    console.log('done!');
  })
  .catch(console.error)
```

See the [composer][] documentation for more details, or to create bug reports related to running or registering tasks.


## API

### .task

Register a task

**Params**

* `name` **{String}**: Task name to register (tasks are cached on `app.tasks`)
* `dependencies` **{String|Array|Function}**: String, list or array of tasks. 
* `callback` **{Function}**: Function to be called when the task is executed. Task functions should either return a stream or call the callback to let [composer][] know when the task is finished.

**Examples**

Register a task.

```js
app.task('default', function() {
  // return the stream to signal "done"
  return app.src('pages/*.hbs')
    .pipe(app.dest('dist'));
});
```

Register a task with dependencies (other tasks to run before executing the task):

```js
app.task('site', ['styles'], function() {
  return app.src('pages/*.hbs')
    .pipe(app.dest('dist'));
});

app.task('default', ['site']);
```

**Get a task**

```js
const task = app.task('site');
```

### .build

Run a task or array of tasks.


**Promise examples**

```js
// run the "default" task, if defined
app.build();
app.build('default');

// run an array of tasks
app.build(['foo', 'bar'])
  .then(() => console.log('done!'))
  .catch(console.error);
```


**Callback examples**

```js
// run the "default" task, if defined
app.build(function(err, results) {
  if (err) return console.error(err);
  console.log(results);
});

app.build('default', function(err, results) {
  if (err) return console.error(err);
  console.log(results);
});

app.build(['foo', 'bar'], function(err, results) {
  if (err) return console.error(err);
  console.log(results);
});
```

### .series

Compose task or list of tasks into a single function that runs the tasks in series.

**Params**

* `tasks` **{String|Array|Function}**: List of tasks by name, function, or array of names/functions.
* `returns` **{Function}**: Composed function that may take a callback function.

**Example**

```js
app.task('foo', function(cb) {
  console.log('this is foo');
  cb();
});

const build = app.series('foo', function(cb) {
  console.log('this is bar');
  cb();
});

build(function(err) {
  if (err) return console.error(err);
  console.log('finished');
});
//=> this is foo
//=> this is bar
//=> finished
```

### .parallel

Compose task or list of tasks into a single function that runs the tasks in parallel.

**Params**

* `tasks` **{String|Array|Function}**: List of tasks by name, function, or array of names/functions.
* `returns` **{Function}**: Composed function that may take a callback function.

**Example**

```js
app.task('foo', function(cb) {
  setTimeout(function() {
    console.log('this is foo');
    cb();
  }, 500);
});

const build = app.parallel('foo', function(cb) {
  console.log('this is bar');
  cb();
});

build(function(err) {
  if (err) return console.error(err);
  console.log('finished');
});
//=> this is bar
//=> this is foo
//=> finished
```

## Events

The following events are emitted by [composer][]. See the composer docs for more details

### on.task

Emitted when a `task` is `register`, `starting` and `finished`.

```js
app.on('task', function(task) {
  console.log(task.status);
  //=> 'register'
});
```

### on.build

Emitted when a `build` is `starting` and `finished`.

```js
app.on('build', function(build) {
  console.log(build.status);
  //=> 'starting'
});
```

## History

### v2.0.0

- Bumped [composer][] to v2.0.0.

### v0.3.0

- Bumped [composer][] to v0.11.0, so the `.watch` method is no longer included by default. To add `.watch`, use the [base-watch][] plugin.