As per this forum post, thanks to Sabroso and Castor, <a href="" target="_blank">Problem - Resetting Calendar Elements on a Search Form</a>

1. Download the “Reset Button” plugin

2. Create new “Reset Button” field which is added to the form where is the calendar field

3. Edit the Reset Button field and in the bottom right hand corner there is an arrow you can click on to open the section called Stuff. Here you can give a CSS class to your button ( btn-primary, etc if your using a Bootstrap 3 template), and also insert this JavaScript in the JS section:



var defaultText = null;



alert("Hello World");

return false;



4. Replace name_of_your_calendar_field with the name of your calendar field.