reactjs.org.switch.lang.user.js

// ==UserScript==
// @name         reactjs.org switch languages
// @version      0.1
// @description  keep the browseing path when switch language on reactjs.org
// @author       Leonard Lin <https://github.com/gwokae>+
// @updateURL    https://gist.github.com/gwokae/77a896865deea912591092167ae3cb00/raw/reactjs.org.switch.lang.user.js
// @match        https://*.reactjs.org/*
// @grant        none
// ==/UserScript==

const DELAY = 1000;
(function() {
  'use strict';
  let qs = getQueryString();
  let debounceId;
  document.addEventListener('click', ({target}) => {
    let el = target
    if (!el.matches('a[href]')) {
      el = el.closest('a[href]');
    }
    if(!el) return;
    const current = getQueryString(el);
    if(current === '/languages') {
      if(debounceId) {
        clearTimeout(debounceId);
      }
      debounceId = setTimeout(updateHref(qs, function(){ debounceId = 0 }), DELAY);
    } else if (current) {
      qs = current;
    }
  });
})();

function updateHref(qs, done) {
  return function() {
    Array
      .from(document.querySelectorAll('a[href][lang]'))
      .forEach((el) => {
        if(el.href.endsWith('reactjs.org/')) {
          el.href = el.href.slice(0, el.href.length - 1) + qs;
        }
      });
  }
}

function getQueryString({origin, href} = document.location) {
  if(origin && href) {
    return href.replace(origin, '');
  }
}