code: function( world ){
  
              // subscribe the .behave() method to the position integration step
              world.on('integrate:positions', this.behave, this);
  
              if ( window.PointerEvent ) {
  
                  this.el.addEventListener('pointerdown', this.grab);
                  window.addEventListener('pointermove', this.move);
                  window.addEventListener('pointerup', this.release);
  
              } else {
  
                  this.el.addEventListener('mousedown', this.grab);
                  this.el.addEventListener('touchstart', this.grab);
  
                  window.addEventListener('mousemove', this.move);
                  window.addEventListener('touchmove', this.move);
  
                  window.addEventListener('mouseup', this.release);
                  window.addEventListener('touchend', this.release);
  
              }
          }
docs: extended