[jQuery] Drag&Drop-Plugin

/*
 * LICENSE: "THE BEER-WARE LICENSE" (Revision 42)
 * <gregor.mitzka@gmail.com> wrote this file. As long as you retain this notice you
 * can do whatever you want with this stuff. If we meet some day, and you think
 * this stuff is worth it, you can buy me a beer in return Gregor Mitzka
 * 
 * @package      jQuery Drag&Drop-Plugin
 * [USER=136855]@author[/USER]       Gregor Mitzka <gregor.mitzka@gmail.com>
 * [USER=51092]@Copyright[/USER]    2013 (C) Gregor Mitzka
 * @version      1.0
 * [USER=60124]@license[/USER]      The Beer-Ware License
 */
(function ( $ ) {
  $.fn.drop = function ( handler, observe ) {
    if ( typeof handler !== 'function' ) {
      throw 'handler must be a function';
    }

    var $this = $( this );

    $( document ).off( 'dragstart dragend' ).on({
      'dragstart': function () {
        $( '[dropzone]' ).addClass( 'droppable-dragging' );
      },

      'dragend' : function () {
        $( '[dropzone]' ).removeClass( 'droppable-dragging droppable-hover' );
      }
    });
    
    var events = {
      'dragover': function ( e ) {
        e.preventDefault();
        e.stopPropagation();
        
        return false;
      },

      'dragenter': function ( e ) {
        e.preventDefault();
        e.stopPropagation();
        
        $this.removeClass( 'droppable-dragging' ).addClass( 'droppable-hover' );
        return false;
      },

      'drop': function ( e ) {
        var data = e.originalEvent.dataTransfer;
        var ret;

        e.preventDefault();
        e.stopPropagation();

        // will return the data for "text/plain" if you try to stringify the Clipboard object
        data.valueOf = function () {
          return this.getData( 'text/plain' );
        };
        // call the callback function for the drop event
        // mostly you will not return any value, but if you do, we will recognize it
        $( '[dropzone]' ).removeClass( 'droppable-dragging droppable-hover' );
        return ( ( ret = handler.call( e.target, data, e ) ) === undefined || !!ret );
      },

      'dragleave': function ( e ) {
        e.preventDefault();
        e.stopPropagation();
        
        $this.removeClass( 'droppable-hover' ).addClass( 'droppable-dragging' );
        return false;
      }
    };

    // observe the list of matched elements by the selector string if observe is true
    if ( observe == null || observe ) {
      $this.parent().delegate( this.selector, events );
    // bind only to the matching elements, that currently exist
    } else {
      $this.on( events );
    }

    return this;
  };
})( jQuery );

// 1. Argument: Callback-Funktion
// 2. Argument: Gibt an, ob auf neue Elemente, die hinzugefügt wurden und dem Auswahl-Pattern entsprechen, auch das Plugin angewendet werden soll: true für ja, ansonsten false. true ist voreingestellt.
$('div').drop(function (data, e) {
  // "data" enthält das Clipboard-Objekt, welches die übertragenen Daten enthält
  // "e" enthält das originale "drop"-Event, welches als jQuery-Event verpackt ist
  // "this" verweist auf das HTML-Element, auf welches die Daten abgelegt wurden
}, true);