Calendar popup for web form

I require a pop-up calendar to appear next to a date field, when a button (of eg. a calendar) next to the date field is selected. Both the web form and the javascript calendar have already been developed. (The javascript calendar is partially dynamically created using PHP, however knowledge of PHP shouldn't be necessary.) I therefore require a small amount of coding in the web form and javascript calendar which allows the calendar to pop-up once a button is selected (and wherein the calendar closes when a different part of the web page is selected or a date on the calendar is selected). Also, of course I required the date selected in the calendar to be transferred to the relevant date field on the web form. Thanks.