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D3js selection.each () callback group argument

Simple html:

 <div class="div1">
      <div class="test"><span>1</span></div>
      <div class="test"><span>2</span></div>
 </div>

And js:

var el = d3.select(".div1").selectAll(".test");
el.each(function() { 
      console.log(arguments);
});

Conclusion:

[undefined, 0, 0]
[undefined, 1, 0]

What is the last argument (0)? According to the source code, this is a group, but I can not find anything about selector groups in the d3 documentation.

Thank.

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1 answer

This is for nested selectors: http://bost.ocks.org/mike/nest/

eg. for this HTML:

<table>
    <tr>
        <td></td>
        <td></td>
    </tr>
    <tr>
        <td></td>
        <td></td>
    </tr>
</table>

Let me choose td:

var el = d3.selectAll("tr").selectAll("td");

el [ Array[2] , Array[2] ]

and el.each:

el.each(function() { 
    console.log('args',arguments);
});

Conclusion:

args [undefined, 0, 0]
args [undefined, 1, 0]
args [undefined, 0, 1]
args [undefined, 1, 1]
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