JavaScript test to identify all elements with a width or min-width style that break the window width (e.g. cause horizontal scroll bar).

FindWideElems.js

// http://stackoverflow.com/a/22638396/1026023 - added try/catch
function css(a) {
    var sheets = document.styleSheets, o = [];
    a.matches = a.matches || a.webkitMatchesSelector || a.mozMatchesSelector || a.msMatchesSelector || a.oMatchesSelector;
    for (var i in sheets) {
        var rules = sheets[i].rules || sheets[i].cssRules;
        for (var r in rules) {
            var m = 0;
            try {
              m = a.matches(rules[r].selectorText);
            } catch (e) { }
            if (m) {
                o.push(rules[r].cssText);
            }
        }
    }
    return o;
}

var all = document.getElementsByTagName("*"), i = 0, rect;
for (; i < all.length; i++) {
    var rules = css(all[i])+"";
    var w = 0;
    if (rules.match(/min\-width\s*:\s*(\d+)px/)) w = rules.match(/min\-width\s*:\s*(\d+)px/)[1];
    if (rules.match(/\swidth\s*:\s*(\d+)px/)) w = rules.match(/\swidth\s*:\s*(\d+)px/)[1];
    if (all[i].getBoundingClientRect().left + w > $(window).width()) {
      all[i].style.outline = "1px solid red";
      console.log(all[i]);
    }
}