function enqueue(self, toEnqueue) {

// If the send queue hasn't been initialized yet, do it, and install an

// event handler that flushes the send queue after binding is done.

if (!self._sendQueue) {

self._sendQueue = [];

self.once('listening', function() {

// Flush the send queue.

for (var i = 0; i < this._sendQueue.length; i++)

this.send.apply(self, this._sendQueue[i]);

this._sendQueue = undefined;

});

if (!self._queue) {

self._queue = [];

self.once('listening', clearQueue);

}

self._sendQueue.push(toEnqueue);

self._queue.push(toEnqueue);

return;

}

function clearQueue() {

const queue = this._queue;

this._queue = undefined;

// Flush the send queue.

for (var i = 0; i < queue.length; i++)

queue[i]();

}

// valid combinations

// send(buffer, offset, length, port, address, callback)

// send(buffer, offset, length, port, address)

// If the socket hasn't been bound yet, push the outbound packet onto the

// send queue and send after binding is complete.

if (self._bindState != BIND_STATE_BOUND) {

enqueue(self, [list, port, address, callback]);

enqueue(self, self.send.bind(self, list, port, address, callback));

return;

}

this.callback(err, sent);

}

Socket.prototype.close = function(callback) {

if (typeof callback === 'function')

this.on('close', callback);

if (this._queue) {

this._queue.push(this.close.bind(this));

return this;

}

this._healthCheck();

this._stopReceiving();

this._handle.close();