First, I found that HTML5 drag and drop is convenient.

http://www.w3schools.com/html/html5_draganddrop.asp

But it's not supported in iOS7 as follows.

https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/HandlingEvents/HandlingEvents.html

In the same document, Apple says drag and drop can be implemented from the basic touch events following the tutorial of the following. But I can't find any clue in there.

https://developer.apple.com/library/safari/documentation/InternetWeb/Conceptual/SafariVisualEffectsProgGuide/InteractiveControl/InteractiveControl.html#//apple_ref/doc/uid/TP40008032-CH16-SW7

After then, I searched and found some tips.
One is "create customized event" but I don't understand how his claim is to be true. (Anyway, createEvent() is deprecated. customEvent constructor is to be used instead.)

http://stackoverflow.com/questions/5186441/javascript-drag-and-drop-for-touch-devices

http://www.sitepoint.com/javascript-custom-events/

Another one is to use some libraries and I don't like that idea.

http://www.gotproject.com/blog/post2.html

https://github.com/timruffles/ios-html5-drag-drop-shim/blob/master/ios-drag-drop.js

And I looked through the source code of the above drag-and-drop-shim and found that there is a method document.elementFromPoint().
I guess that this method can be used to implement drag and drop.