var str, matches, i, ii, count;
str = $("body").html();
matches = str.match(/id=".+"/g);

for (i = 0; i < matches.length; i += 1) {
    count = 0;
    for (ii = 0; ii < matches.length; ii += 1) {
        if (matches[i] === matches[ii]) {
            count += 1;
        }
    }
    if (count > 1) {
        console.log("ID: " + matches[i] + " is used more then once!");
    }
}