preventScroll not working reliabily

ajax.js

var ajax = (function() {
    // Private
    var httpRequest, data,
        ajaxState = {
            isDone :    4,
            isOkay :    200
        },
    successHandler = function(data) {
        var json = JSON.parse(data);
        getRandomKey(json);
    },
    errorHandler = function() {
        console.log("Error: Status is not reporting 'Okay'");
    },
    getRandomKey = function(array) {
        var totalKeys = array.length;

        if (totalKeys > 0) {
            var randomKey = random(totalKeys);
        }
        templify(array[randomKey], ".headline");
    },
    templify = function(entry, element) {
        var container = document.querySelector(element);
        container.innerHTML = entry;
    },
    random = function(int) {
        return Math.floor(Math.random() * int);
    };

    // Public
    var makeRequest = function(method, url) {
        if (window.XMLHttpRequest) {
            httpRequest = new XMLHttpRequest();
        } else if (window.ActiveXObject) {
            try {
                    httpRequest = new ActiveXObject("Msxml2.XMLHTTP");
                }
                catch (e) {
                    try {
                        httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
                    }
                    catch (e) {}
                    }
        }
        httpRequest.open(method, url, true);
        httpRequest.onreadystatechange = function () {
            if (httpRequest.readyState === ajaxState.isDone) {
                if (httpRequest.status === ajaxState.isOkay) {
                    data = httpRequest.responseText;
                    successHandler(data);
                } else {
                    errorHandler();
                }
            }
        };
        httpRequest.send();
    };

    return {
        request: makeRequest
    };

})();

preventScroll.js

var preventScroll = (function() {

    var resize = function(el) {
        var element = document.querySelector(el),
            style = window.getComputedStyle(element), // element.style.fontSize doesn't work
            fontsize = parseFloat(style.fontSize);
            // console.log(document.body.scrollHeight + " > " window.innerHeight);
        while (document.body.scrollHeight > window.innerHeight) {
            fontsize = fontsize - 1; // For some reason 'fontsize--;' doesn't work
            element.style.fontSize = fontsize + 'px';
        }
    };

    return {
        resize: resize
    };

})();