google-play-music-song-iterator.js

var loopThroughSongsAnd = function(doThis, interval, runMax) {
    console.time('Looping through songs');

    var getIntOrDefault = function(variable, defaultValue) {
        variable = parseInt(variable, 10);
        if (isNaN(variable) || !variable) {
            variable = getIntOrDefault(defaultValue, 0);
        }
        return variable;
    }

    interval = getIntOrDefault(interval, 1);
    runMax = getIntOrDefault(runMax, 1000);

    var mainPanel = document.querySelector("#mainContainer");
    var mainPanelRectangle = mainPanel.getClientRects()[0];
    mainPanel.scrollTop = 0;
    var runCount = 0;
    var song;

    var loopInterval = window.setInterval(function() {
        if (!song || !song.nextElementSibling) {
            song = document.querySelector('.song-table tr.song-row');
            if (!song.nextElementSibling) {
                console.warn('Could not find next song after ', song);
                stopLooping();
            }
        }
        var songRectangle = song.getClientRects()[0];
        if (songRectangle.bottom >= mainPanelRectangle.bottom) {
            mainPanel.scrollTop = Math.min(
                mainPanel.scrollTop + songRectangle.top - mainPanelRectangle.top,
                mainPanel.scrollHeight - mainPanel.clientHeight
            );
        }
        if (!song.nextElementSibling.classList.contains('song-row')) {
            console.log('Reached last song');
            stopLooping();
        }
        if (!doThis(song)) {
            stopLooping();
        } else {
            song = song.nextElementSibling;
        }
        runCount++;
        if (runCount >= runMax) {
            console.error('Reached run count maximum of', runMax);
            stopLooping();
        }
    }, interval);

    var stopLooping = function() {
        window.clearInterval(loopInterval);
        console.timeEnd('Looping through songs');
    };
};