Question

My form has a textarea and a submit button. The textarea is used to input HTML code and I want to use JavaScript (JQuery) to validate the input with regex. If multiple html tags have the same id value, the entire source is printed on the page with the offending tags marked red.

Answer 1

You could use this snippet:

See DEMO

var isValid = true;
$('[id]').each(function() {
    if ($('[id="'+this.id+'"]').length > 1) {
        isValid = false;
        return false;
    }
});

alert(isValid);​