javascript - Displaying Clickable Grid -

what's best way display grid below allow user select multiple boxes , have page capture selected elements?

the existing code working seems inadequate since displays grid of buttons 1 can selected:

<tr>  <th>6-8 am</th>  <td><button type="button" class="btn"></button></td>  <td><button type="button" class="btn"></button></td>  <td><button type="button" class="btn"></button></td>  <td><button type="button" class="btn"></button></td>   <td><button type="button" class="btn"></button></td>       <td><button type="button" class="btn"></button></td>    <td><button type="button" class="btn"></button></td>                                     </tr>

write function capture onclick , store against variable of data of element , send server when user wants synchronize