Drupal 8  8.0.2
/var/www/d8/core/misc/progress.js

A progressbar object. Initialized with the given id. Must be inserted into the DOM afterwards through progressBar.element.

Method is the function which will perform the HTTP request to get the progress bar state. Either "GET" or "POST".

pb = new Drupal.ProgressBar('myProgressBar'); some_element.appendChild(pb.element);

Parameters
{string}id
{function}updateCallback
{string}method
{function}errorCallback