Combine promises in task queues of individual concurrency setting, and compose task queues to more complex sequences or procedures easily.
npm install concurrent-task-queuejavascript
var queue = require('concurrent-task-queue');
//promise html image
function getImage(url) {
return new Promise(function (resolve, reject) {
var image = new Image();
image.src = url;
image.onload = function() {
resolve(image);
};
image.onerror = function(e) {
resolve(e);
}
});
}
//a task is a promise returning function (needed to avoid the promise to proceed immediately)
var tasks = [
()=>getImage("http://www.free-emoticons.com/files/funny-emoticons/7279.png"),
()=>getImage("http://www.free-emoticons.com/files/funny-emoticons/7278.png"),
()=>getImage("http://www.free-emoticons.com/files/funny-emoticons/7277.png"),
()=>getImage("http://www.free-emoticons.com/files/funny-emoticons/7276.png"),
()=>getImage("http://www.free-emoticons.com/files/funny-emoticons/7275.png"),
()=>getImage("http://www.free-emoticons.com/files/funny-emoticons/7274.png"),
()=>getImage("http://www.free-emoticons.com/files/funny-emoticons/7273.png"),
()=>getImage("http://www.free-emoticons.com/files/funny-emoticons/7272.png"),
()=>getImage("http://www.free-emoticons.com/files/funny-emoticons/7271.png"),
()=>getImage("http://www.free-emoticons.com/files/funny-emoticons/7270.png")
];
//queue returns a promise returning function. tasks is an array of promise returning functions, and concurrent
//is the max. number of tasks to be executed in parallel
//create queue of images to load (max. 5 simultaneously)
var loadimages = queue(tasks, 5);
/*
//note that every queue is a promise returning function, ergo a task!
//for that queues can be composed to other queues, each with an individual
//setting for concurrency, ultimately allowing to describe complex sequences of
//async procedures easily.
var transformimages = queue(transformtasks, 1);
var sequence = queue([loadimages, transformimages], 1)
/ /
//invoke queue sequence
loadimages().then(function(result) {
result.forEach(function(elem) {
if(elem instanceof Image)
document.body.appendChild(elem);
console.log(elem);
})
}).catch(function(e) { console.log(e) });
``