Question

I’m new to prototype, but fairly experienced with jQuery so it could just be I’m misunderstanding how prototype works. I’m trying to do the following

$$("tr.total_line td.total_cell").first().replace(newTotal);

but I’m getting TypeError: Cannot read property 'firstChild' of null

When I execute $$("tr.total_line td.total_cell").first() in the JS console I get a DOM element result.

Here’s the relevant markup

<tr class="total_line">
    <td colspan="2">Total</td>
    <td class="total_cell">$50.00</td>
    <td></td>
</tr>

Answer 1

Since .first() is returning a <td> element, you’ll need to insert a <td> or <th> in order for the replacement to be valid HTML.

So if newTotal is:

"<td>$100</td>"

…it should work. But if it is just:

"$100"

…it doesn’t.

Or another option would be to replace the innerHTML of the <td>:

$$("tr.total_line td.total_cell").first().innerHTML = newTotal;