jquery plugin: check if a scrollbar has been scrolled 50% of overall height

check-scrollbar-scrolled.jquery.js

$.fn.scrollCheck = function(options) {
    var has_read_textarea = false;
    textarea = $(this);
    textarea.scroll(function() {
        if ((textarea.scrollTop() + textarea.height()) >= (textarea[0].scrollHeight/2)) {
            has_read_textarea = true;
        }
    });
    var textarea_timeout = window.setInterval(function() {
        if (has_read_textarea !== false) {
            window.clearTimeout(textarea_timeout);
            if (options.doNext) {
                options.doNext();
            }
        }
    }, options.timeout || 10000);
};

usage

$("#test").scrollCheck({
    timeout: 100,
    doNext: function() {
       $('#continue').show();
    }
});