How can I hide an HTML table row <tr> so that it takes up no space?

You can set <tr id="result_tr" style="display: none;"> and then show it back with JavaScript:

var result_style = document.getElementById('result_tr').style;
result_style.display = 'table-row';

Can you include some code? I add style="display:none;" to my table rows all the time and it effectively hides the entire row.