queue-batch

A minimalistic queue processor which emits events.

Example

``javascript
var Processor = require('queue-batch');

var longRunningFunction = (item, next) => {
console.log('got a new item to process');
console.log(item);
setTimeout(next, 1000);
};

var processor = new Processor(longRunningFunction);
processor.on('error', (error) => {
console.error('an error occured', error);
});
processor.on('empty', () => {
console.log('queue exhausted');
});

processor.push('item');
processor.push('one', 'two');
processor.concat([1, 2, 3]);
`
Which will output
`bash
got a new item to process
item
got a new item to process
one
got a new item to process
two
got a new item to process
1
got a new item to process
2
got a new item to process
3
`
Then after a second or so
`bash
queue exhausted
`

API

new Processor(callback, concurrency = 10, queue = []);

* callback: function(item, next: function(error)) is a required function which will be invoked for each item pushed or concated to the processor.
* currency: ?int is an optional positive integer, decribing the number of concurrent items can be handled by the callback.
* queue: ?Array is an optional array. If specified the items will automatically be added to the queue and the processor will start working.

Creates a new batch processor with a handler callback, optional concurrency limit and queue. The batch processor is an EventEmitter and will emit an empty even, when the queue has been completed. If at any point the callback function returns an error to the next callback option the error event will be emitted on the processor object.

Processor.prototype.push(item1[, item2[, ...itemn]]);

* item1 ... itemn each argument provided will be push onto the queue. If the batch processor is not running at the concurrency limit the first item will immediately start getting processed.

Processor.prototype.concat(array);

* array' is an array of items to push onto the queue one after the other.

This has the same effect as processor.push(array[0], ... , array[n]); or array.forEach((item) => processor.push(item));

Processor.prototype.on(eventName, handler);

* eventName: 'error' | 'empty' the event to which you wish to attach a handler
* handler: function the desired handler function.

Events

error - processor.on('error', function (error) { });

Emitted if an errors has been reported back via the processor callback function through the next callback.

``javascript
var errorCallback = (item, next) => {
if (item === 2) { return next('2 is an exceptional number'); }
next();
};
var processor = new Processor(errorCallback);
processor.on('error', (error) => {
console.error(error); // outputs '2 is an exceptional number'
});
`

empty - processor.on('empty', function () { });`

Emitted when the queue no longer contains any items.