This worked for me.

var iframes = $('iframe');



$('button').click(function() {

    iframes.attr('src', function() {

        return $(this).data('src');

    });

});



iframes.attr('data-src', function() {

    var src = $(this).attr('src');

    $(this).removeAttr('src');

    return src;

});

jsFiddle.