How to pass data to parent window from popup window?

Question

How can I pass some data or call a function on the parent window from a popup window?

The user will click a link which will open a popup on the same website, once he is

Answer 1

Here is a fun and easy demo that is heavily inspired by this answer to a similar question (but modified for my own purposes to help investigate the most difficult bug of my career).

Create 2 files (in the same directory) as follows:

parent.html

Add My Card
=>
No data yet.    

popup.html

    
    
        
            http://date.jsontest.com/
        
        
            http://time.jsontest.com/
        
        
            http://md5.jsontest.com/?text=HereIsSomeStuff