SOURCE CODE: Uize.Widget.Drag.Move (view docs)

/*______________
|       ______  |   U I Z E    J A V A S C R I P T    F R A M E W O R K
|     /      /  |   ---------------------------------------------------
|    /    O /   |    MODULE : Uize.Widget.Drag.Move Class
|   /    / /    |
|  /    / /  /| |    ONLINE : http://www.uize.com
| /____/ /__/_| | COPYRIGHT : (c)2005-2016 UIZE
|          /___ |   LICENSE : Available under MIT License or GNU General Public License
|_______________|             http://www.uize.com/license.html
*/

/* Module Meta Data
  type: Class
  importance: 1
  codeCompleteness: 100
  docCompleteness: 2
*/

/*?
  Introduction
    The =Uize.Widget.Drag.Move= class wires a drag-and-drop behavior to a node to let the user move its position, with support for different position units.

    *DEVELOPERS:* `Chris van Rensburg`
*/

Uize.module ({
  name:'Uize.Widget.Drag.Move',
  required:'Uize.Dom.Basics',
  builder:function  (_superclass) {
    'use strict';

    var
      /*** Variables for Scruncher Optimization ***/
        _Uize_Dom_Basics = Uize.Dom.Basics
    ;

    /*** Private Instance Methods ***/
      function _getNodeToMove (m) {
        return m.getNode (m._shellNode) || m.getNode ();
      }

    return _superclass.subclass ({
      alphastructor:function () {
        var
          m = this,
          _sideNames = [
            ['left','right'],
            ['top','bottom']
          ],
          _dragSides = [],
          _dragSideUnits = [],
          _dragStartNodePos = []
        ;
        m.wire ({
          'Drag Start':
            function () {
              var _node = _getNodeToMove (m);
              function _captureAxisStartInfo (_axis) {
                function _getPosUnit (_posStr) {
                  var _unitMatch = _posStr.match (/(px|%)\s*$/);
                  return _unitMatch ? _unitMatch [1] : 'px';
                }
                var
                  _axisSideNames = _sideNames [_axis],
                  _dragSide = _dragSides [_axis] = _node.style [_axisSideNames [1]] ? 1 : 0,
                  _dragSidePosStr = _Uize_Dom_Basics.getStyle (_node,_axisSideNames [_dragSide]),
                  _dragSideUnit = _getPosUnit (_dragSidePosStr)
                ;
                _dragStartNodePos [_axis] = _dragSideUnit == '%' ? (parseFloat (_dragSidePosStr) / 100 * _node.offsetParent ['offset' + (_axis ? 'Height' : 'Width')]) : parseFloat (_dragSidePosStr);
                _dragSideUnits [_axis] = _getPosUnit (_node.style [_axisSideNames [_dragSide]]);
              }
              _captureAxisStartInfo (0);
              _captureAxisStartInfo (1);
            },
          'Drag Update':
            function () {
              var _node = _getNodeToMove (m);
              function _setAxisPos (_axis) {
                var
                  _dragSide = _dragSides [_axis],
                  _dragSideUnit = _dragSideUnits [_axis],
                  _dragSidePos = (_dragStartNodePos [_axis] + m.eventDeltaPos [_axis] * (_dragSide ? -1 : 1))
                ;
                if (_dragSideUnit == '%')
                  _dragSidePos = _dragSidePos / _node.offsetParent ['offset' + (_axis ? 'Height' : 'Width')] * 100
                ;
                _node.style [_sideNames [_axis] [_dragSide]] = _dragSidePos + _dragSideUnit;
              }
              _setAxisPos (0);
              _setAxisPos (1);
            }
        });
      },

      stateProperties:{
        _shellNode:'shellNode'
      }
    });
  }
});