如何在一条又一条路径上显示d3中的过渡？

var svg = d3.select("body")
            .append("svg")
            .attr("width", width)
            .attr("height", height);

var path = svg.append("path")
              .datum(data)
              .attr("d", d3.line()
                           .x(function(d) { return x(d.x); })
                           .y(function(d) { return y(d.y); })
              );

path.transition()
    .duration(2000)
    .attrTween("stroke-dasharray", function() {
        var length = path.node().getTotalLength();
        return function(t) {
            return (d3.interpolateString("0," + length, length + ",0"))(t);
        };
    });