VietMX Staff asked 4 years ago
<script>– HTML parsing is blocked, the script is fetched and executed immediately, HTML parsing resumes after the script is executed.<script async>– The script will be fetched in parallel to HTML parsing and executed as soon as it is available (potentially before HTML parsing completes). Useasyncwhen the script is independent of any other scripts on the page, for example, analytics.<script defer>– The script will be fetched in parallel to HTML parsing and executed when the page has finished parsing. If there are multiple of them, each deferred script is executed in the order they were encountered in the document. If a script relies on a fully-parsed DOM, thedeferattribute will be useful in ensuring that the HTML is fully parsed before executing. There’s not much difference in putting a normal<script>at the end of<body>. A deferred script must not containdocument.write.
Note: The async and defer attributes are ignored for scripts that have no src attribute.
