Load queue

Designed to allow running task in a queue with parallel support. Can be used for image (package) or file loading.

* Small library: 6kb minified.
* Simple queue with custom task defined with simple function

Queues types:

1. Queue - Standard load queue, the default export.
2. CachedQueue -- Cached load queue - when adding already loaded url, it will not use queue and call success immediately (errors are not cached)

Install

``
npm install load-queue --save
`

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Library is exported via UMD. From LoadQueue object you can access to default queue, Queue and CachedQueue.

`html



`

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#### Default (Queue)
`javascript
import Queue from 'load-queue'

var queue = new Queue(loaderTask)
`

#### Queue
`javascript
import {Queue} from 'load-queue'

var queue = new Queue(loaderTask)
`

#### CachedQueue
`javascript
import {CachedQueue} from 'load-queue'

var queue = new CachedQueue(loaderTask)
`

Usage

Before constructing queue, you must provide your own task implementation. The function will accept 3 arguments:
1. entry - An QueueEntry with an url entry.url
2. success - A callback that accepts any custom arguments that will be passed to your custom callback
3. failure - A callback for failure that accepts an error Error object

`javascript
/**
* @param {QueueEntry} entry
* @param {function} success
* @param {function} failure
*/
var loaderTask = function (entry, success, failure) {
// ... loading entry.url
setTimeout(function () {
if (entry.url === 'url1') {
failure(new Error('Failed!'))
} else {
success('my custom var', 'custom var 2')
// or just success()
}
}, 1000)
}
`

__Queue construct accepts:__
1. The task function.
2. Number of concurrent jobs that can be ran (default 1).
3. start timeout - defines if the start will use timeout function to throttle calls and
give time for start -> cancel use case (when user scrolls in list and etc). Set null to turn it off.
Default is 50ms (which is enough for fast scroll)

`javascript
var queue = new Queue(loaderTask)
// or
var queue = new Queue(loaderTask, 2)
// or
var queue = new CachedQueue(loaderTask)
`

To add a new url to load queue, just call add(url, success, error). The add method will return the QueueEntry that holds
given url.

`javascript
var entry = queue.add('url', function(url, customVar, customVar2) {
console.log(url, customVar, customVar2)
}, function(error) {
console.log(error)
})
console.log(entry.url)

// Or cancel the request
entry.cancel()
`

#### QueueEntry
You can access to url and the cancel method. For internal use you can access to running task entry.task and call
success/error callbacks (the callbacks that that executes).

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You can cancel given url from queue at any time (even when loading - the callbacks wont be called).
There are 2 ways how to cancel request.

1. Calling cancel(url) on queue object. Like queue.cancel('test.cz')
2. Calling cancel() on QueueEntry from add function.

#### Task cancel
If your task implementation needs to handle the cancel (like cancel the http request) then the queue will use it's own
logic and then call cancel on the task.

`javascript
var loaderTask = function (entry, success, failure) {
// ... loading entry.url
var timeout = setTimeout(function () {
if (entry.url === 'url1') {
failure(new Error('Failed!'))
} else {
success('my custom var', 'custom var 2')
// or just success()
}
}, 5000)

// Cancel the timeout
this.cancel = function () {
clearTimeout(timeout)
}
}
``

Copyright and License

load-queue
was written by Martin Kluska and is released under the
MIT License.

Copyright (c) 2017 Martin Kluska