@LinkXSystem

直接翻源码lib/event.js

// By default EventEmitters will print a warning if more than 10 listeners are
// added to it. This is a useful default which helps finding memory leaks.
var defaultMaxListeners = 10;

Object.defineProperty(EventEmitter, 'defaultMaxListeners', {
  enumerable: true,
  get: function() {
    return defaultMaxListeners;
  },
  set: function(arg) {
    // force global console to be compiled.
    // see https://github.com/nodejs/node/issues/4467
    console;
    // check whether the input is a positive number (whose value is zero or
    // greater and not a NaN).
    if (typeof arg !== 'number' || arg < 0 || arg !== arg)
      throw new TypeError('"defaultMaxListeners" must be a positive number');
    defaultMaxListeners = arg;
  }
});