core-js is the more common of the two in our index: it runs on 17,404 websites against 76 for SweetAlert, and 29 sites use both. Counts come from real scans, not vendor claims.
core-js is a modular standard library for JavaScript, with polyfills for cutting-edge ECMAScript features.
SweetAlert is a JavaScript library that provides alternative alert and modal dialog boxes for web applications, with customisable features, aiming to improve the user interface of the default browser dialogs.
29 sites run both core-js and SweetAlert. That is 38% of the sites using SweetAlert, the smaller of the two.
Want to know which one a particular site uses? Look it up and see its whole stack, or compare two sites side by side.