Check for duplicate id values in a html page From http://webmasters.stackexchange.com/questions/16901/check-for-duplicate-id-values-in-a-html-page

find_duplicate_id_in_doom.js

(function findDuplicateIds() {
    var ids = {};
    var all = document.all || document.getElementsByTagName("*");
    for (var i = 0, l = all.length; i < l; i++) {
        var id = all[i].id;
        if (id) {
            if (ids[id]) {
                console.log("Duplicate id: #" + id);
            } else {
                ids[id] = 1;
            }
        }
    }
})();