<script>

<div class="dln" itemprop="articleBody"><div class="shdw top"> </div><p><a class="URI" href="https://html.spec.whatwg.org/multipage/scripting.html#attr-script-async" target="_blank" rel="noopener nofollow ugc">https://html.spec.whatwg.org/multipage/scripting.html#attr-script-async</a>
</p><div class="shdw btm"> </div><button type="button" class="mxmz icn_ btn_mxmz"></button></div>

WHATWGによる<script>の読込のタイミングを示した図

defer

<div class="dln" itemprop="articleBody"><div class="shdw top"> </div><p><a class="URI" href="https://qiita.com/phanect/items/82c85ea4b8f9c373d684" target="_blank" rel="noopener nofollow ugc">https://qiita.com/phanect/items/82c85ea4b8f9c373d684</a>
</p><div class="shdw btm"> </div><button type="button" class="mxmz icn_ btn_mxmz"></button></div>

『<script> タグに async / defer を付けた場合のタイミング』

async

<div class="dln" itemprop="articleBody"><div class="shdw top"> </div><p><a class="URI" href="https://html.spec.whatwg.org/multipage/scripting.html" target="_blank" rel="noopener nofollow ugc">https://html.spec.whatwg.org/multipage/scripting.html</a>
</p><div class="shdw btm"> </div><button type="button" class="mxmz icn_ btn_mxmz"></button></div>

t_wの輪郭

<script>

WHATWGによる<script>の読込のタイミングを示した図

defer

『<script> タグに async / defer を付けた場合のタイミング』

async

『4.12 Scripting - HTML Standard』