Function point

explainshell/web/static/js/d3.v3.js:501–506

()

        type: "dragstart"
      });
      function point() {
        var p = target.parentNode;
        return touchId != null ? d3.touches(p).filter(function(p) {
          return p.identifier === touchId;
        })[0] : d3.mouse(p);
      }
      function dragmove() {
        if (!target.parentNode) return dragend();
        var p = point(), dx = p[0] - origin_[0], dy = p[1] - origin_[1];