How to get Unix timestamp using Bootstrap-datetimepicker

I am using 3rd party date time picker from https://eonasdan.github.io/bootstrap-datetimepicker/

It is working fine, however, I'd like to get the value in Unix timestamp format. How do I do that? There is no formatting option for Unix. https://eonasdan.github.io/bootstrap-datetimepicker/Functions/#format

function getValue() {
    var date = $('#datetimepicker1').data('date');
    alert(date); // shows 05/25/2017 5:43 PM
}


<div class='input-group date' id='datetimepicker1'>
    <input type='text' class="form-control" />
    <span class="input-group-addon">
        <span class="glyphicon glyphicon-calendar"></span>
    </span>
</div>