Frontend & browser·Loading, assets and the critical path
the analytics script downloaded alongside the HTML and ran the moment it arrived, whenever that was.
async script
Also calledasync attribute
A script that downloads in parallel with parsing and executes as soon as it is ready, interrupting the parser at an unpredictable point. Execution order between async scripts is whatever the network decides, so it is only safe for independent scripts with no dependencies. It still blocks the main thread when it runs, so an async third-party script can still delay the first paint.