Javascript, Checkbox checked limit

I want to limit checked checkboxes to 3, I couldn't do it if you can help that'd be a great favour.

        <div class="col-md-4" dir="ltr" ><center>
<span class="button-checkbox">
    <button type="button" style="width:200px;text-align: left;" class="btn" data-color="primary">'.$icon_image.' '.$group.' </button>
    <input type="checkbox" name="icon[]" value='.$sgid.'  />
</span>