Skip to content

Instantly share code, notes, and snippets.

@paolorossi
Last active December 17, 2021 04:36
Show Gist options
  • Save paolorossi/5747533 to your computer and use it in GitHub Desktop.
Save paolorossi/5747533 to your computer and use it in GitHub Desktop.
Javascript Queue for sequencing AJAX requests and other asynchronous tasks. Demo http://jsfiddle.net/rusci/26Dud/6/
// Queue class for serializing AJAX calls.
//
// Inspired by Raynos http://stackoverflow.com/a/4797596/1194060
//
// Queue has a public append method that expects some kind of task.
// A task is a generic function passed as callback.
// Constructor expects a handler which is a method that takes a ajax task
// and a callback. Queue expects the handler to deal with the ajax and run
// the callback when it's finished
function Queue(handler) {
var queue = [];
function run() {
var callback = function () {
queue.shift();
// when the handler says it's finished (i.e. runs the callback)
// We check for more tasks in the queue and if there are any we run again
if (queue.length > 0) {
run();
}
}
// give the first item in the queue & the callback to the handler
handler(queue[0], callback);
}
// push the task to the queue. If the queue was empty before the task was pushed
// we run the task.
this.append = function (task) {
queue.push(task);
if (queue.length === 1) {
run();
}
}
}
// small handler that launch task and calls the callback
// when its finished
var queue = new Queue(function (task, callback) {
task(function () {
// call an option callback from the task
if (task.callback)
task.callback();
// call the buffer callback.
console.log(task, ' done');
callback();
});
});
// Test
// Add some tasks to queue...
var tasks = [
function (callback) {
setTimeout(function () {
$('output').insert({
bottom: '<li>Step 1 - ' + new Date() + '</li>'
});
callback();
}, 1000);
},
function (callback) {
setTimeout(function () {
$('output').insert({
bottom: '<li>Step 2 - ' + new Date() + '</li>'
});
callback();
}, 3000);
},
];
for (i = 0; i < tasks.length; i++) {
queue.append(tasks[i]);
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment