tumblr_blog_subs_default.user.js

// ==UserScript==
// @name         Tumblr Blog Subs Default
// @namespace    gist.github.com/marcustyphoon
// @version      0.2
// @description  Forces the default Tumblr dashboard tab to "Blog Subs"
// @author       marcustyphoon
// @match        https://www.tumblr.com/*
// @grant        none
// @noframes
// ==/UserScript==

/* globals tumblr */
/* eslint-disable no-unmodified-loop-condition */

(async function () {
  'use strict';

  let retries = 0;
  while (typeof tumblr === 'undefined' || typeof tumblr.navigate === 'undefined') {
    if (retries++ > 1000) return;
    await new Promise((resolve) => setTimeout(resolve));
  }

  const attemptRedirect = () => {
    if (
      ['/dashboard', '/'].includes(location.pathname) &&
      document
        .querySelector('main > :is([data-timeline], [data-timeline-id])')
        ?.matches(
          '[data-timeline^="/v2/timeline/dashboard"], [data-timeline^="/v2/tabs/for_you"], [data-timeline-id="/dashboard/following"], [data-timeline-id="/dashboard/stuff_for_you"]',
        )
    ) {
      tumblr.navigate('/dashboard/blog_subs');
    }
  };

  attemptRedirect();

  new MutationObserver(attemptRedirect).observe(document.getElementById('root'), {
    childList: true,
    subtree: true,
    attributeFilter: ['data-timeline', 'data-timeline-id'],
  });
})();