One of common tasks I often do with web crawlers is fire requests concurrently. This will go fine if you are only interested in the responses. If you are interested in finding out what request the response was coming from, then it is problematic because we only see Response object in fullfilled callback.

SteamAnalyst is a site that shows market data for virtual items which get traded and sold on Steam platform. It’s primary and only focus at the moment is CS:GO market. Traders use this site to easily check an item’s price or their inventory value, but developers use their API to correctly price items on their commercial projects.