Improve the readability on Pocket (formerly Read it Later).

pocket_readability.user.js

// ==UserScript==
// @name Pocket Readability
// @version 1.3
// @author Matt Slack
// @description Improve the readability on Pocket (formerly Read it Later).
// @match https://getpocket.com/a/*
// ==/UserScript==

// Stolen from https://developer.mozilla.org/en-US/docs/DOM/CSSStyleSheet/insertRule
function addStylesheetRules(decls) {
  "use strict";
  var decl, dl, i, j, rl, rule, rulesStr, s, selector, style = document.createElement('style');
  document.getElementsByTagName('head')[0].appendChild(style);
  if (!window.createPopup) { /* For Safari */
    style.appendChild(document.createTextNode(''));
  }
  s = document.styleSheets[document.styleSheets.length - 1];
  for (i = 0, dl = decls.length; i < dl; i++) {
    j = 1;
    decl = decls[i];
    selector = decl[0];
    rulesStr = '';
    if (Object.prototype.toString.call(decl[1][0]) === '[object Array]') {
      decl = decl[1];
      j = 0;
    }
    for (rl = decl.length; j < rl; j++) {
      rule = decl[j];
      rulesStr += rule[0] + ':' + rule[1] + (rule[2] ? ' !important' : '') + ';\n';
    }

    if (s.insertRule) {
      s.insertRule(selector + '{' + rulesStr + '}', s.cssRules.length);
    } else { /* IE */
      s.addRule(selector, rulesStr, -1);
    }
  }
}

function fix_dashes(e) {
  var endash = new RegExp('(\\d)(-)(\\d)', 'gm'),
    emdash = new RegExp('(\\s+)(--|—)(\\s+)?', 'gm'),
    apostrophe = new RegExp('([A-Za-z])\'([a-z])', 'gm'),
    open_dumbquote = new RegExp('(\\s|^)(\')', 'gm'),
    close_dumbquote = new RegExp('(\')(\\s|"|$)', 'gm'),
    open_doubledumbquote = new RegExp('(\\s|"|^)(")', 'gm'),
    close_doubledumbquote = new RegExp('(")(\\s|$)', 'gm'),
    widont = new RegExp('(\\s)([^\\s]+)$'),
    ellipses = new RegExp('(\\.(\\s)?\\.(\\s)?\\.)', 'gm');

  return e.textContent.replace(apostrophe, "$1’$2")
    .replace(open_dumbquote, "$1‘")
    .replace(close_dumbquote, "’$2")
    .replace(open_doubledumbquote, "$1“")
    .replace(close_doubledumbquote, "”$2")
    .replace(endash, '$1–$3')
    .replace(emdash, "\u200a—\u200a")
    .replace(widont, "\u00a0$2")
    .replace(ellipses, "…");
}

function textNodesUnder(el) {
  var n, a=[], walk=document.createTreeWalker(el,NodeFilter.SHOW_TEXT,null,false);
  n = walk.nextNode();
  while(n){ a.push(n); n = walk.nextNode();}
  return a;
}

function init() {
  "use strict";
  var reader = document.getElementById('page_reader');

  if (reader !== null) {
    for (var i of textNodesUnder(reader)){
      (i).textContent = fix_dashes(i);
    }

    addStylesheetRules([
      ['#page_reader.readability',
        ['text-rendering', 'optimizeLegibility'],
        ['-webkit-font-feature-settings', "'kern' 1, 'liga' 1, 'onum' 1, 'pnum', 'frac'"]
        ],
      ['.readability.font-serif .text_body p',
        ['font-family', 'ETBookOT, Andada, "OFL Sorts Mill Goudy","Hoefler Text", Georgia, serif']
        ],
      ['.readability.font-serif .reader_content',
        ['font-family', 'ETBookOT, Andada, "OFL Sorts Mill Goudy","Hoefler Text", Georgia, serif']
        ],
      ['.readability.font-sans .text_body strong',
        ['font-family', 'Thonburi, Helvetica, Arial, sans-serif']
        ],
      ['.readability.font-sans .text_body p',
        ['font-family', 'Thonburi, Helvetica, Arial, sans-serif']
        ],
      ['.pkt-nav',
        ['opacity', '0'],
        ['-webkit-transition', 'opacity .2s ease-in-out'],
        ['transition', 'opacity .2s ease-in-out']
        ],
      ['.pkt-nav:hover',
        ['opacity', '1']
        ],
      ['figcaption',
        ['margin', '0 0 2em'],
        ['font-size', '60%']
        ]
    ]);
    reader.classList.add('readability');
  }
}

var readyStateCheckInterval = setInterval(function () {
  "use strict";
  if (document.readyState === "complete") {
    init();
    clearInterval(readyStateCheckInterval);
  }
}, 10);