Change the drag mode.
@param {string} mode - The new drag mode.
@returns {Cropper} this
function setDragMode(mode) {
    var options = this.options,
        dragBox = this.dragBox,
        face = this.face;

    if (this.ready && !this.disabled) {
      var croppable = mode === DRAG_MODE_CROP;
      var movable = options.movable && mode === DRAG_MODE_MOVE;
      mode = croppable || movable ? mode : DRAG_MODE_NONE;
      options.dragMode = mode;
      setData(dragBox, DATA_ACTION, mode);
      toggleClass(dragBox, CLASS_CROP, croppable);
      toggleClass(dragBox, CLASS_MOVE, movable);

      if (!options.cropBoxMovable) {
        // Sync drag mode to crop box when it is not movable
        setData(face, DATA_ACTION, mode);
        toggleClass(face, CLASS_CROP, croppable);
        toggleClass(face, CLASS_MOVE, movable);
      }
    }

    return this;
  }