Problem when textarea's id contain colon (:) character

<textarea id="formEditor:textEditor" name="formEditor:textEditor" style="visibility: hidden; display: none; ">Content Here </textarea>

function saveData(id) {
    try {
        eval('var data = CKEDITOR.instances.' + id + '.getData();');
        document.getElementById(id).innerHTML = data;
        alert(data);
    } catch (ex) {
        alert('Exception: '+ex);
    }
}