Frontend & browser·Loading, assets and the critical path
the script downloaded in parallel but waited to run until the document had finished parsing.
defer script
Also calleddefer attribute
A script that downloads without blocking parsing and executes after the document is parsed, in document order, before `DOMContentLoaded`. It is the right default for application code: parallel download, predictable order, no parser blocking. Module scripts are deferred automatically, which is why an inline module and a classic script can run in a surprising order.