18

<input type="checkbox" name="checkbox_name[]" id="checkbox_name_1" />1<br />
<input type="checkbox" name="checkbox_name[]" id="checkbox_name_2" />2<br />
<input type="checkbox" name="checkbox_name[]" id="checkbox_name_3" />3<br />
<input type="checkbox" name="checkbox_name[]" id="checkbox_name_4" />4<br />
<input type="checkbox" name="checkedAll" id="checkedAll"/>全选/取消全选

演示地址