Greasemonkey script that show title and artist of the music now playing at Amazon Music.

amazon-music-show-now-playing.js

// ==UserScript==
// @name     amazon-music-now-playing
// @namespace llf
// @include /^https://music\.amazon\.co\.jp/
// @version  1
// @grant    none
// ==/UserScript==

function charWidth(str) {
  var w = 0;
  for (var i = 0; i < str.length; i++) {
   	if (escape(str.charAt(i)).startsWith('%u')) {
      w += 2;
    } else {
      w += 1;
    }
  }
  return w;
}

var width = 20;
var count = 0;

var prevTitle = '';

window.setInterval(function() {
  var titleElem = document.querySelector('.trackTitle>a>span');

  if (titleElem !== null) {
    var artistElem = document.querySelector('.trackArtist>a>span');
 		var nowPlaying = document.querySelector('.playButton').classList.contains('playerIconPause');
  
    var title = titleElem.innerText + " [" + artistElem.innerText + "]";
    
    var slicedTitle = charWidth(title) >= width ? (title + "　" + title).substr(count, width) : title;
    document.title = (nowPlaying ? '▶ ' : '❚❚ ') + slicedTitle;
    
    count++;
    if (count > title.length) {
      count = 0;
    }
    
    if (prevTitle !== title) {
    	count = 0;
      
      document.querySelector('link[rel="icon"]').href = document.querySelector('.renderImage').dataset.src;
    }
    prevTitle = title;
  }
}, 200);