Bookmarklet to Autoscroll Webpages (with commands)

auto_scroll_bookmarklet.js

javascript: (function () {
    let _ss_interval_pointer;
    let _ss_speed = 1;
    let _ss_speed_pairs = [
        [0, 0],
        [1, 200.0],
        [1, 120.0],
        [1, 72.0],
        [1, 43.2],
        [1, 25.9],
        [2, 31.0],
        [4, 37.2],
        [8, 44.8],
        [8, 26.4],
        [16, 32.0]
    ];
    let _ss_last_onkeypress = document.onkeypress;
    _ss_stop = function() {
        clearTimeout(_ss_interval_pointer)
    };
    _ss_start = function() {
        _ss_abs_speed = Math.abs(_ss_speed);
        _ss_direction = _ss_speed / _ss_abs_speed;
        _ss_speed_pair = _ss_speed_pairs[_ss_abs_speed];
        _ss_interval_pointer = setInterval('scrollBy(0,' + _ss_direction * _ss_speed_pair[0] + '); if((pageYOffset<=1)||(pageYOffset==document.height-innerHeight)) _ss_speed=0;', _ss_speed_pair[1]);
    };
    _ss_adj = function(q) {
        _ss_speed += q;
        if (Math.abs(_ss_speed) >= _ss_speed_pairs.length) _ss_speed = (_ss_speed_pairs.length - 1) * (_ss_speed / Math.abs(_ss_speed))
    };
    _ss_quit = function() {
        _ss_stop();
        document.onkeypress = _ss_last_onkeypress;
    };
    document.onkeypress = function(e) {
        if ((e.charCode == 113) || (e.keyCode == 27)) {
            _ss_quit();
            return;
        };
        if (e.charCode >= 48 && e.charCode <= 57) _ss_speed = e.charCode - 48;
        else switch (e.charCode) {
            case 95:
                _ss_adj(-2);
            case 45:
                _ss_adj(-1);
                break;
            case 43:
                _ss_adj(2);
            case 61:
                _ss_adj(1);
                break;
        };
        _ss_stop();
        _ss_start();
    };
    _ss_stop();
    _ss_start();
})();


/*
0-9	: Set scroll speed, 0 being stand-still and 9 being skim-speed
–	:   Decrease speed
=	:   Increase speed
q	:   Quit

Credit: http://tim.theenchanter.com/2008/08/autoscroll-in-safari-firefox.html
*/