Prepend an anchor tag inside elements with IDs to easily get permalinks to document fragments e.g., https://domain.tld/#my-id

bookmarklet.js

javascript:Array.from(document.querySelectorAll("[id]")).forEach(e=>{if(/[A-Za-z][-A-Za-z0-9_:.]*/.test(e.id)&&!e.querySelector(`a[href="#${e.id}"]`)){const r=document.createElement("a");r.innerHTML="#",r.href=`#${e.id}`,e.insertBefore(r,e.firstChild)}});

index.js

// Optionally change the initial selector e.g., only headers: "h1, h2, h3, h4, h5, h6"
Array.from(document.querySelectorAll("[id]")).forEach($el => {
  // ID looks legit and there isn't already a link to it (within the found element)
  if (/[A-Za-z][-A-Za-z0-9_:.]*/.test($el.id) && !$el.querySelector(`a[href="#${$el.id}"]`)) {
    const $link = document.createElement("a")
    $link.innerHTML = "#"
    $link.href = `#${$el.id}`
    $el.insertBefore($link, $el.firstChild)
  }
})