tumblr-no-reblogs.user.js

// ==UserScript==
// @name        Tumblr No Reblogs
// @match       https://*.tumblr.com/*
// @version     1.0
// @author      mdashlw
// @run-at      document-start
// @inject-into page
// ==/UserScript==

const _fetch = unsafeWindow.fetch;

function patchResponse(response, patcher) {
  const _json = response.json;
  response.json = async function () {
    const json = await _json.call(this);
    patcher(json);
    return json;
  };
  return response;
}

unsafeWindow.fetch = function () {
  const url = arguments[0];

  if (typeof url === "string") {
    if (url.includes("/posts?fields") && url.includes("&context=archive")) {
      return _fetch.apply(this, arguments).then((response) =>
        patchResponse(response, (json) => {
          const posts =
            json.response.posts?.filter((post) => !post.rebloggedRootId) ?? [];

          if (!posts.length && json.response.posts?.length) {
            posts.push(json.response.posts[0]);
          }

          json.response.posts = posts;
        }),
      );
    }
  }

  return _fetch.apply(this, arguments);
};