1 // type can be namespaced, e.g., "click.foo"

     2 // listener can be null for removal

     3 d3_selectionPrototype.on = function(type, listener, capture) {

     4   if (arguments.length < 3) capture = false;

     5 

     6   // parse the type specifier

     7   var name = "__on" + type, i = type.indexOf(".");

     8   if (i > 0) type = type.substring(0, i);

     9 

    10   // if called with only one argument, return the current listener

    11   if (arguments.length < 2) return (i = this.node()[name]) && i._;

    12 

    13   // remove the old event listener, and add the new event listener

    14   return this.each(function(d, i) {

    15     var node = this;

    16 

    17     if (node[name]) node.removeEventListener(type, node[name], capture);

    18     if (listener) node.addEventListener(type, node[name] = l, capture);

    19 

    20     // wrapped event listener that preserves i

    21     function l(e) {

    22       var o = d3.event; // Events can be reentrant (e.g., focus).

    23       d3.event = e;

    24       try {

    25         listener.call(node, node.__data__, i);

    26       } finally {

    27         d3.event = o;

    28       }

    29     }

    30 

    31     // stash the unwrapped listener for retrieval

    32     l._ = listener;

    33   });

    34 };