YouTube speed rememberer

Remembers playback speed.
Versione datata 14/02/2018. Vedi la nuova versione l'ultima versione.
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// ==UserScript==
// @name         YouTube speed rememberer
// @version      0.3.1
// @description  Remembers playback speed.
// @author       gvvad
// @match        *.youtube.com/*
// @run-at       document-end
// @namespace https://greasyfork.org/users/100160
// ==/UserScript==

(function() {
    'use strict';
    var PLAYER_CLASSNAME = "#movie_player";
    
    //set button on video player
    //_msg - lable string
    var setLabel = function(_msg, _mp) {
        var label = document.querySelector("#_ytp-label");
        if (_msg === undefined) {
            if (label) label.parentElement.removeChild(label);
            return;
        }
        if (label) {
            label.innerText = _msg;
            return;
        }
        var cls = document.querySelector(PLAYER_CLASSNAME).querySelector(".ytp-right-controls");

        var span = document.createElement('span');
        span.setAttribute('id','_ytp-label');
        span.setAttribute('class','ytp-button');
        span.onclick = function() {
            _mp.setPlaybackRate(1);
        };
        span.innerText = _msg;

        cls.insertBefore(span, cls.firstChild);
    };
    
    //set or remove button
    //_rate - play rate
    var setSpeedLabel = function(_rate, _mp) {
        if (_rate == 1) {
            setLabel();
        } else {
            setLabel('x' + _rate, _mp);
        }
    };

    var rate = 1.0;
    rate = parseFloat(localStorage.getItem("pl-rate"));
    rate = (isNaN(rate))? 1.0 : rate;

    //modificate player object and store play rate
    //mp - movieplayer object
    var worker = function(mp) {
        if (rate != 1.0) {
            mp.setPlaybackRate(rate);
            setSpeedLabel(mp.getPlaybackRate(), mp);
        }

        mp.addEventListener("onPlaybackRateChange", function(){
            localStorage.setItem("pl-rate", mp.getPlaybackRate());
            setSpeedLabel(mp.getPlaybackRate(), mp);
        });
    };

    //Watchdog for youtube video-player object
    var _count = 25;
    var hInterval = setInterval(function() {
        var buf = document.querySelector(PLAYER_CLASSNAME);
        if (buf || !(_count--)) {
            clearInterval(hInterval);
            worker(buf);
        }
    }, 200);
})();