> That means the browser stops parsing the HTML mid-way through the page load, resolves the CDN's domain to IP, does a TLS handshake and establishes a connectio

> That means the browser stops parsing the HTML mid-way through the page load, resolves the CDN's domain to IP, does a TLS handshake and establishes a connection to the CDN, waits to download the script, parses, runs it, and then proceeds on to the rest of the HTML. This is not true since about 2008. All major browsers parse the HTML without waiting for synchronous <script> to load. https://developer.mozilla.org/en-US/docs/Glossary/speculative_parsing https://developer.mozilla.org/en-US/docs/Glossary/speculativ... If the <script> uses document.write() and what's written contains unbalanced tags, or if the document is modified in some other ways, then they re-parse but that combination is rare. This page explains what to avoid to ensure re-parsing doesn't happen (the rules may differ with other browsers): https://developer.mozilla.org/en-US/docs/Glossary/speculative_parsing https://developer.mozilla.org/en-US/docs/Glossary/speculativ...