A content delivery network or content distribution network (CDN) is a large distributed system of proxy servers deployed in multiple data centers via the Internet. The goal of a CDN is to serve content to end-users with high availability and high performance.
With CDNJS, the shop owner on Shopify will save time for upload also as storage space on Shopify.
I tested and has found that speed from CDNJS high than CDN from Shopify.
You can find more than information about this service at http://cdnjs.com/about.
Huynh Mai Anh Kiet