Tech Challenge

A site loads a JavaScript library from a third-party CDN. Which mechanism makes the browser refuse to execute the file if the CDN was compromised and the file's bytes were altered?

<script src="https://cdn.example.com/lib.js"
        integrity="sha384-oqVuAfXRKap7fdgcCY5uykM6+R9GqQ8K/uxy9rx7HNQlGYl1kPzQho1wx4JwY8wC"
        crossorigin="anonymous"></script>