For example, How could I put `debugger;` after `.attr("class", "bar")`
So that I can debug at the breakpoint

Thanks

Before
------

```
svg.selectAll(".bar")
    .data(data)
  .enter()
    .append("rect")
    .attr("class", "bar")
    .style("fill", function(d) { return color(d.num); })
    .attr("x", function(d) { return x(d.letter); })
    .attr("width", x.rangeBand())

```

I expect I can debug like this
------------------------------

```
svg.selectAll(".bar")
    .data(data)
  .enter()
    .append("rect")
    .attr("class", "bar")
    .debugger;
    .style("fill", function(d) { return color(d.num); })
    .attr("x", function(d) { return x(d.letter); })
    .attr("width", x.rangeBand())

```

UPDATE
------

I got the error `Uncaught TypeError: undefined is not a function`

```
$.fn.debug = function() { debugger; return this; };

 group.selectAll("path") // bind data to empty collection as usual
        .data([data]) // what need another [] to bracket it ?
        .enter()
        .append("path")
        .debug()
        .attr("d", line)

```