var fragment = (
    <div class="dialog_element">
        <div class="title">Titel des Eintrags:</div>
        <div class="content">
            <input type="text" name="entry_title_line" class="line_input" id="entry_title_line"/>
        </div>
    </div>
    <div class="dialog_element">
        <div class="title">Beschreibung:</div>
        <div class="content" >
            <textarea name="entry_desc_box" class="box_input" id="entry_desc_box"></textarea>
        </div>
    </div>
    )



    var entry_title_line = fragment.getElementById('entry_title_line');

--> fragment.getElementById is not a function