HTML

https://htmlreference.io

Spec

One-page https://html.spec.whatwg.org

Multipage https://html.spec.whatwg.org/multipage

HTML 5.2 (2017) https://www.w3.org/TR/html52

HTML 5.3 (2021) https://www.w3.org/TR/html53

Learn

https://web.dev/learn/html/

<script> element

https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script

warning

The browser blocks parsing and rendering of the page when it encounters <script> elements without a defer or async attribute - source

async and defer

Scripts loaded from <script> elements with a type=module attribute are deferred by default - source

Difference: https://stackoverflow.com/questions/10808109/script-tag-async-defer

Omit type='text/javascript' in <script> tags

https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#attr-type

This is not recommended: <script type='text/javascript'>/* JS code */</script>

HTML5 specification urges authors to omit the attribute rather than provide a redundant MIME type.