Auto-number table rows?

I have the following HTML table:

<table border="1">
  <tr>
    <td>blue</td>
  </tr>
  <tr>
    <td>red</td>
  </tr>
  <tr>
    <td>black</td>
  </tr>
</table>

I would like each row in this table have a number automatically assigned to each item.

How could he do?

The following CSS enumerates table rows (demo):

table {
  counter-reset: rowNumber;
}

table tr::before {
  display: table-cell;
  counter-increment: rowNumber;
  content: counter(rowNumber) ".";
  padding-right: 0.3em;
  text-align: right;
}

<table cellpadding="0">
  <tr><td>blue</td></tr>
  <tr><td>red</td></tr>
  <tr><td>yellow</td></tr>
  <tr><td>green</td></tr>
  <tr><td>purple</td></tr>
  <tr><td>orange</td></tr>
  <tr><td>maroon</td></tr>
  <tr><td>mauve</td></tr>
  <tr><td>lavender</td></tr>
  <tr><td>pink</td></tr>
  <tr><td>brown</td></tr>
</table>

If the CSS cannot be used, try the following JavaScript code (demo):

var table = document.getElementsByTagName('table')[0],
  rows = table.getElementsByTagName('tr'),
  text = 'textContent' in document ? 'textContent' : 'innerText';

for (var i = 0, len = rows.length; i < len; i++) {
  rows[i].children[0][text] = i + ': ' + rows[i].children[0][text];
}

<table border="1">
  <tr>
    <td>blue</td>
  </tr>
  <tr>
    <td>red</td>
  </tr>
  <tr>
    <td>black</td>
  </tr>
</table>

And if you would use headers as well the following is the thing you need: [http://jsfiddle.net/davidThomas/7RyGX/][1]

table {
    counter-reset: rowNumber;
}

table tr:not(:first-child) {
    counter-increment: rowNumber;
}

table tr td:first-child::before {
    content: counter(rowNumber);
    min-width: 1em;
    margin-right: 0.5em;
}

note the: ":not(:first-child)" in there. [1]: http://jsfiddle.net/davidThomas/7RyGX/

Here is a modification of David Thomas' CSS solution that works with or without a header row in the table. It increments the counter on the first td cell of each row (thereby skipping the row with only th cells):

table
{
    counter-reset: rowNumber;
}

table tr > td:first-child
{
    counter-increment: rowNumber;
}
                
table tr td:first-child::before
{
    content: counter(rowNumber);
    min-width: 1em;
    margin-right: 0.5em;
}

You can see the behavior in this jsfiddle.

Here's a javascript solution that will add a cell at the beginning of each row , this cell will be used for numbering, if there is a th cell this gets a colspan=2 attribute.

var addNumeration = function(cl){
  var table = document.querySelector('table.' + cl)
  var trs = table.querySelectorAll('tr')
  var counter = 1
  
  Array.prototype.forEach.call(trs, function(x,i){
    var firstChild = x.children[0]
    if (firstChild.tagName === 'TD') {
      var cell = document.createElement('td')
      cell.textContent = counter ++
      x.insertBefore(cell,firstChild)
    } else {
      firstChild.setAttribute('colspan',2)
    }
  })
}

addNumeration("test")

<table class="test" border="1">
  <tr>
   <th>hi!</th>
  </tr>
  <tr>
    <td>blue</td>
  </tr>
  <tr>
    <td>red</td>
  </tr>
  <tr>
    <td>black</td>
  </tr>

</table>