task-list

Simple utility library for managing a list of tasks and their lifecycle with support for promises and Node.js-style callbacks.

Installation

npm install task-list --save

Overview

The task-list module is used to orchestrate starting and stopping tasks in sequential order.

Each task is provided as an object that provides a start function and an optional stop function.

If your task is asynchronous then your start/stop function can either invoke a callback or return a promise. If returning a promise, then your start/stop function should have no arguments. If not using promises for your asynchronous operation, then your function should declare a single callback argument which will be a Node.js-style callback that you can invoke to indicate success or failure.

If your task is synchronous then make sure your start/stop function does not declare any arguments. As long as the function doesn't return something that looks like a Promise then it will be assumed that your task completed synchronously.

Usage

Simple example with minimal configuration:

var tasks = require('task-list').create([
    {
        name: 'asynchronous-task',
 
        // if you want to use callback for your async operation then
        // your function should have one argument which will be the
        // callback function
        start: function(callback) {
            // do something
            callback();
        },
 
        // NOTE: "stop" functional is optional
        // if you want to use callback for your async operation then
        // your function should have one argument which will be the
        // callback function
        stop: function(callback) {
            // do something
            callback();
        }
    },
 
    {
        name: 'asynchronous-task-using-promise',
 
        start: function() {
            // return a Promise
            return new Promise(function(resolve, reject) {
                setTimeout(function() {
                    resolve();
                }, 10);
            });
        }
    },
 
    {
        name: 'synchronous-task',
 
        // synchronous operations should be declared as a function
        // with no arguments
        start: function() {
            // all we need to do is return if our task is synchronous
        }
    }
]);
 
// Using callback-style to start/stop all tasks
tasks.startAll(function(err) {
    if (err) {
        // some error occurred
    } else {
        // tasks are running
    }
 
    // now stop the tasks
    tasks.stopAll(function(err) {
        if (err) {
            // one or more services failed to stop
        } else {
            // all services stopped successfully
        }
    });
});
 
// startAll and stopAll can also be invoked with no argument if you
// would rather use promises.
tasks.startAll().then(function() {
    // now stop the tasks and return the Promise that it creates
    return tasks.stopAll();
}).then(function() {
    console.log('All tasks were started and have now been stopped');
}).catch(function(err) {
    throw err;
})

An example that provides a logger:

var options = {
    logger: {
        info: function(message) {
            console.log('INFO: ' + message);
        },
 
        success: function(message) {
            console.log('SUCCESS: ' + message);
        },
 
        error: function(message) {
            console.error('ERROR: ' + message);
        }
    }
};
 
var services = require('task-list').create([
    {
        name: 'task1',
 
        start: function() {
            // do something
        }
    }
], options);

API

Method: create(tasks, options)

Returns a TaskList which has operations for controlling the lifecycle of the tasks

options

• logger: An object that has info, success, or error properties which should be functions that expect a single message argument. The info, success, and error properties are optional and if not provided then the corresponding log level will not produce any output.

Example:

var tasks = require('task-list').create(tasksArray, options)

Class: TaskList

A TaskList is returned by call to require('task-list').create(...).

NOTE: If you call startAll or stopAll without a callback argument then a Promise will be returned. The Promise implementation will be the native Promise provided by the JavaScript runtime environment or the Promise implementation that your application exposed as a global. If there is no global Promise implementation found, then you will encounter exceptions.

Method: startAll([callback])

This method is used to start all of the tasks that belong to this TaskList. If a callback is provided then it is expected to be a Node.js-style callback that will be invoked when all tasks have been started or error occurred. If a callback is not provided then a Promise will be returned.

Method: stopAll([callback])

This method is used to stop all of the tasks that belong to this TaskList. If a callback is provided then it is expected to be a Node.js-style callback that will be invoked when all tasks have been stopped or error occurred. If a callback is not provided then a Promise will be returned.