[原]点击按钮，表格隔行变色：偶数行为黄色背景，奇数行为默认颜色。通过table的getElementsByTagName取得所有的tr，依次遍历，如果是偶数就…………。

window.onload = function () {

document.getElementById('btn').onclick = function () {
                var trs = document.getElementById('tb').getElementsByTagName('tr');
                for (var i = 0; i < trs.length; i++) {
                    if (i % 2 != 0) {
                        trs[i].style.backgroundColor = 'yellow';
                    } else {
                        trs[i].style.backgroundColor = '';
                    }
                }
            };
        };
<input type="button" name="name" value="变色" id="btn" />
    <table id="tb" border="1" cellpadding="0" cellspacing="0">
        <tr>
            <td>
            AAAAAAAAAAAAAAAAAA
            </td>
              <td>
            AAAAAAAAAAAAAAAAAA
            </td>
              <td>
            AAAAAAAAAAAAAAAAAA
            </td>
        </tr>
        <tr>
            <td>
            AAAAAAAAAAAAAAAAAA
            </td>
              <td>
            AAAAAAAAAAAAAAAAAA
            </td>
              <td>
            AAAAAAAAAAAAAAAAAA
            </td>
        </tr>
        <tr>
            <td>
            AAAAAAAAAAAAAAAAAA
            </td>
              <td>
            AAAAAAAAAAAAAAAAAA
            </td>
              <td>
            AAAAAAAAAAAAAAAAAA
            </td>
        </tr>
        <tr>
            <td>
            AAAAAAAAAAAAAAAAAA
            </td>
              <td>
            AAAAAAAAAAAAAAAAAA
            </td>
              <td>
            AAAAAAAAAAAAAAAAAA
            </td>
        </tr>
</table>