I would format this a bit differently. If you don't mind:

```js
function d3_svg_lineStep(points) {
  var i = 0, n = points.length, p0, p1 = points[0], path = [p1[0], ",", p1[1]];
  while (++i < n) {
    p0 = p1, p1 = points[i];
    path.push("H", (p0[0] + p1[0]) / 2, "V", p1[1], "H", p1[0]);
  }
  return path.join("");
}
```