function find_diff_class(classes) {
    return classes.split(/\s+/).find(x => x.match(/.diff\d.*/));
}

$(document).ready(function() {
    $('.diff').mouseover(function() {
        let c = find_diff_class($(this).attr('class'))
        $('.' + c).addClass('diff-highlight')
    });
    $('.diff').mouseout(function() {
        let c = find_diff_class($(this).attr('class'))
        $('.' + c).removeClass('diff-highlight')
    });
});