1 d3.dispatch = function() {

     2   var dispatch = new d3_dispatch(),

     3       i = -1,

     4       n = arguments.length;

     5   while (++i < n) dispatch[arguments[i]] = d3_dispatch_event();

     6   return dispatch;

     7 };

     8 

     9 function d3_dispatch() {}

    10 

    11 d3_dispatch.prototype.on = function(type, listener) {

    12   var i = type.indexOf("."),

    13       name = "";

    14 

    15   // Extract optional namespace, e.g., "click.foo"

    16   if (i > 0) {

    17     name = type.substring(i + 1);

    18     type = type.substring(0, i);

    19   }

    20 

    21   this[type].on(name, listener);

    22 };

    23 

    24 function d3_dispatch_event() {

    25   var listeners = [],

    26       listenerByName = {};

    27 

    28   function dispatch() {

    29     var z = listeners, // defensive reference

    30         i = -1,

    31         n = z.length,

    32         l;

    33     while (++i < n) if ((l = z[i])._on) l.apply(this, arguments);

    34   }

    35 

    36   dispatch.on = function(name, listener) {

    37     var l, i;

    38 

    39     // remove the old listener, if any

    40     if (l = listenerByName[name]) {

    41       l._on = false;

    42       listeners = listeners.slice(0, i = listeners.indexOf(l)).concat(listeners.slice(i + 1));

    43       delete listenerByName[name];

    44     }

    45 

    46     // add the new listener, if any

    47     if (listener) {

    48       listener._on = true;

    49       listeners.push(listener);

    50       listenerByName[name] = listener;

    51     }

    52 

    53     return dispatch;

    54   };

    55 

    56   return dispatch;

    57 };