seqx

Executes tasks sequentially. The result of a task is passed to the next. Returns promises which resolve when tasks are completed. Fires events when tasks are completed.

Installation

Install with npm

npm install seqx --save

Example

var seqx = require("seqx")

task = function (result, id, context) { }
executor = seqx({context: someObj, manual: false});
var taskPromise = executor.add(task);

Tasks

Tasks are functions. A task can receive one or more arguments, in the following order:

1. result The result from the previous task. Can be undefined.
2. id The task's id which is an incrementing counter.
3. context An optional context object which is was supplied when the executor was created.

function task(result, id, context) {
  return valueForNextTask;
 }

API

Create

seq( {context: Object, manual: Boolean} )

• context {Object} - A custom context object which is passed to each task
• manual {Boolean} - If set, start` must be called on the executor to begin task execution.

Creates a sequential executor.

Methods

seq.add(task[,task...])

• task {Function}- task function to be executed
• return {Promise}- A promise which resolves when the task completes and returns the output, if any.

Adds a task to the executor's queue.

seq.addn(task, n)

• task {Function}- task function to be executed
• n {Number} - Number of times to sequentially execute the task. Each time, the output of a previous iteration is provided to the next.
• return {Promise}- A promise which resolves when the task completes and returns the output, if any.

Adds a task multiple times to the executor's queue.

seq.start()

Starts executing tasks on the task queue. Relevant only when the manual: true option is provided to the constructor seq(). start is automatically called for auto start executors.

Events

seqx emits the following events:

on('start', cb())

Emitted when task execution begins.

on('task', cb(fn))

Emitted when a new task is added. The task fn is available as an argument to the event.

on('completed', cb(result, id, context))

Emitted when a task is completed. Callback receives the result of the task, the task id and the context, if any.

on('abort', cb())

Emitted if abort() is called.