d3 selectAll源代码

Question

I'm trying to understand the source code for d3 selectAll and I don't understand the line following my comment below.

I can see how there is a closure on the selector string and that this is set to node when d3_selectAll is invoked, but how are the other three arguments in the call consumed?

import "../core/array";
import "selection";

d3_selectionPrototype.selectAll = function(selector) {
  var subgroups = [],
      subgroup,
      node;

  selector = d3_selection_selectorAll(selector);




for (var j = -1, m = this.length; ++j < m;) {
    for (var group = this[j], i = -1, n = group.length; ++i < n;) {
      if (node = group[i]) {
        //***where are node.__data__, i, j consumed?***
        subgroups.push(subgroup = d3_array(selector.call(node, node.__data__, i, j)));
        subgroup.parentNode = node;
      }
    }
  }



return d3_selection(subgroups);
};

function d3_selection_selectorAll(selector) {
  return typeof selector === "function" ? selector : function() {
    return d3_selectAll(selector, this);
  };
}

Answer 1

This is only relevant in the context of subselections and explained in the documentation :

The selector may also be specified as a function that returns an array of elements (or a NodeList), or the empty array if there are no matching elements. In this case, the specified selector is invoked in the same manner as other operator functions, being passed the current datum d and index i , with the this context as the current DOM element.

In particular, if the selector is not a function, these arguments are simply ignored (function declaration at the end with no arguments).