refactor: simplify the handling of the "drain" event

The two event handlers are merged into one.

lib/socket.ts

@@ -223,25 +223,40 @@ export class Socket extends EventEmitter {
  private setTransport(transport) {
  const onError = this.onError.bind(this);
  const onPacket = this.onPacket.bind(this);
- const flush = this.flush.bind(this);
+ const onDrain = this.onDrain.bind(this);
  const onClose = this.onClose.bind(this, "transport close");
 
  this.transport = transport;
  this.transport.once("error", onError);
  this.transport.on("packet", onPacket);
- this.transport.on("drain", flush);
+ this.transport.on("drain", onDrain);
  this.transport.once("close", onClose);
- // this function will manage packet events (also message callbacks)
- this.setupSendCallback();
 
  this.cleanupFn.push(function () {
  transport.removeListener("error", onError);
  transport.removeListener("packet", onPacket);
- transport.removeListener("drain", flush);
+ transport.removeListener("drain", onDrain);
  transport.removeListener("close", onClose);
  });
  }
 
+ /**
+ * Upon transport "drain" event
+ *
+ * @private
+ */
+ private onDrain() {
+ this.flush();
+
+ if (this.sentCallbackFn.length > 0) {
+ debug("executing batch send callback");
+ const seqFn = this.sentCallbackFn.shift();
+ for (let i = 0; i < seqFn.length; i++) {
+ seqFn[i](this.transport);
+ }
+ }
+ }
+
  /**
  * Upgrades socket to the given transport
  *
@@ -388,31 +403,6 @@ export class Socket extends EventEmitter {
  }
  }
 
- /**
- * Setup and manage send callback
- *
- * @api private
- */
- private setupSendCallback() {
- // the message was sent successfully, execute the callback
- const onDrain = () => {
- if (this.sentCallbackFn.length > 0) {
- debug("executing batch send callback");
- const seqFn = this.sentCallbackFn.shift();
- const l = seqFn.length;
- for (let i = 0; i < l; i++) {
- seqFn[i](this.transport);
- }
- }
- };
-
- this.transport.on("drain", onDrain);
-
- this.cleanupFn.push(() => {
- this.transport.removeListener("drain", onDrain);
- });
- }
-
  /**
  * Sends a message packet.
  *