Polyfill is a service which accepts a request for a set of browser features and returns only the polyfills that are needed by the requesting browser.
Spin.js dynamically creates spinning activity indicators that can be used as resolution-independent replacement for AJAX loading GIFs.
Polyfill.io is leading in Top 10K Sites, Top 100K Sites, Top 1M Sites and The Entire Web.
In terms of market share, Spin JS is clearly lagging behind, losing to Polyfill.io in all segments.
Spin JS has better usage coverage in more websites categories. Including Science & Education, Computers Electronics & Technology, Arts & Entertainment, Travel & Tourism and 13 other categories.
Polyfill.io is leading in Lifestyle, Food & Drink, Law & Government, Business & Consumer Services and 3 other categories.
Polyfill.io is leading in most countries, including United States, United Kingdom, Canada, Japan and 142 other countries.
Spin JS is leading in Russia, Taiwan, Poland, Greece and 15 other countries.