var syncScroll = function() {
    var items = arguments;
    for (var i = 0; i < items.length; i++) {
        items[i].addEventListener('scroll', function() {
            for (var j = 0; j < items.length; j++) {
                if (i !== j) {
                    items[j].scrollTop = this.scrollTop; // this is the element that triggered the event
                }
            }
        });
    }
};

// usage example below
var before = document.getElementsByClassName('before')[0];
var center = document.getElementsByClassName('center')[0];
var after = document.getElementsByClassName('after')[0];
syncScroll(before, center, after); // the order does not matter