Greasemonkey script to add link anchors to Wikipedia page subheadings

wikipedia-subheading-links.user.js

// https://benjeffrey.com/greasemonkey-script-for-wikipedia-subheading-links
// Available under the MPL 2.0
// ==UserScript==
// @key value
// @name        Wikipedia Subheading Links
// @namespace   com.benjeffrey.wikipedia-subheading-links
// @description Add links to subheadings on Wikipedia pages.
// @include http://*.wikipedia.org/*
// @include https://*.wikipedia.org/*
// ==/UserScript==
contentsItems = document.getElementById('toc').getElementsByTagName('li');
for (var i = 0; i < contentsItems.length; i++) {
    subheadingHash = contentsItems[i].getElementsByTagName('a')[0].hash.slice(1);
    subheading = document.getElementById(subheadingHash);
    subheading.innerHTML = ('<a href="#' + subheadingHash + '">' + subheading.innerHTML + ' #</a>');
}