GR_reviews.user.js

// ==UserScript==
// @name        GoodReads Review Management
// @namespace   FeepingCreature@github.com
// @description Show/Hide reviews. State stored between site loads
// @include     */www.goodreads.com/*
// @version     1
// @grant       none
// @require https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js
// ==/UserScript==

var STORAGE_ID = 'greasemonkey goodreads hide state';

function getItemState(dom_id) {
  var item = localStorage.getItem(STORAGE_ID);
  var state = {};
  if (item && item != "") state = JSON.parse(item);
  
  if (state.hasOwnProperty(dom_id) && state[dom_id] == 'hide') return 'hide';
  else return 'show';
}

function setItemState(dom_id, value) {
  var item = localStorage.getItem(STORAGE_ID);
  var state = {};
  if (item && item != "") state = JSON.parse(item);
  
  if (value == 'show') delete state[dom_id];
  else state[dom_id] = value;
  localStorage.setItem(STORAGE_ID, JSON.stringify(state));
}

function showHideReview(dom_id, link) {
  if (getItemState(dom_id) == 'show') hideReview(dom_id, link);
  else showReview(dom_id, link);
}

function hideReview(dom_id, link) {
  $('#'+dom_id).find('.reviewText').hide();
  $('#'+dom_id).fadeTo(0, 0.4);
  setItemState(dom_id, 'hide');
  link.text('[+]');
}

function showReview(dom_id, link) {
  $('#'+dom_id).find('.reviewText').show();
  $('#'+dom_id).fadeTo(0, 1);
  setItemState(dom_id, 'show');
  link.text('[-]');
}

function makeShowHideButtonFor(dom_id) {
  var link = null;
  link = $('<a/>', {
    class: 'right',
    text: '[-]',
    style: 'cursor: pointer;'
  }).on('click', function() { showHideReview(dom_id, link); });
  if (getItemState(dom_id) == 'hide') hideReview(dom_id, link);
  return link;
}

$('.review').each(function() {
  var dom_id = $(this).attr('id');
  $(this).find('.reviewDate').before(makeShowHideButtonFor(dom_id));
});