forEach querySelectorAll
HTML
<table id="table">
<tr>
<td>Foo</td>
</tr>
<tr>
<td>Foo</td>
</tr>
<tr>
<td>Foo</td>
</tr>
<tr>
<td>Foo</td>
</tr>
<tr>
<td>Foo</td>
</tr>
</table>
CSS
.stripe { background: #ccc; }
JavaScript
var each = Array.prototype.forEach;
var rows = document.querySelectorAll("#table tr");
each.call(rows, function(row, i) {
if (!(i % 2)) {
row.className += "stripe";
}
});