Use when.js to run tasks in sequence, parallel, on in a pipeline where the next task receives the result of the previous

run-tasks-examples.js

var when = require('../when');
var delay = require('../delay');

/**
 * Run array of tasks in sequence with no overlap
 * @param tasks {Array} array of task functions
 * @return {Array} result of each task will be in the
 * array position corresponding to position of the
 * task in the tasks array
 */
function sequence(tasks) {
	return when.reduce(tasks, function(results, task) {
		return when(task.call(null), function(result) {
			results.push(result);
			return results;
		});
	}, []);
}

/**
 * Run array of tasks in parallel
 * @param tasks {Array} array of task functions
 * @return {Array} result of each task will be in the
 * array position corresponding to position of the
 * task in the tasks array
 */
function parallel(tasks) {
	return when.map(tasks, function(task) {
		return task.call(null);
	});
}

/**
 * Run array of tasks in a pipeline where the next
 * tasks receives the result of the previous
 * @param tasks {Array} array of task functions
 * @return {*} return value of the final task
 */
function pipeline(tasks, initialValue) {
	return when.reduce(tasks, function(value, task) {
		return task.call(null, value);
	}, initialValue);
}

// Some test tasks
function t1(x) {
	return delay(arguments.length ? (x+1) : 1, 100);
}

function t2(x) {
	return delay(arguments.length ? (x+1) : 2, 50);
}

function t3(x) {
	return delay(arguments.length ? (x+1) : 3, 0);
}

// Example of running them in sequence, in parallel, and in a pipeline
when(sequence([t1, t2, t3]), function(results) { console.log('sequence', results); });
when(parallel([t1, t2, t3]), function(results) { console.log('parallel', results); });
when(pipeline([t1, t2, t3], 0), function(results) { console.log('pipeline', results); });

the-results.txt

parallel [ 1, 2, 3 ]
sequence [ 1, 2, 3 ]
pipeline 3