From c6aeb33855456e160474421d544c2477719184ae Mon Sep 17 00:00:00 2001
From: Brendan Kenny <bckenny@gmail.com>
Date: Tue, 7 Feb 2017 18:07:50 -0800
Subject: [PATCH] perf: gather all event listeners in parallel (#1667)

* issue devtools commands to get event listeners in parallel

* disable websocket compression for cri
---
 lighthouse-core/gather/connections/cri.js             |  4 +++-
 .../gatherers/dobetterweb/all-event-listeners.js      | 11 ++++-------
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/lighthouse-core/gather/connections/cri.js b/lighthouse-core/gather/connections/cri.js
index 377e981d20b8..7eb32c35d778 100644
--- a/lighthouse-core/gather/connections/cri.js
+++ b/lighthouse-core/gather/connections/cri.js
@@ -46,7 +46,9 @@ class CriConnection extends Connection {
       this._pageId = response.id;
 
       return new Promise((resolve, reject) => {
-        const ws = new WebSocket(url);
+        const ws = new WebSocket(url, {
+          perMessageDeflate: false
+        });
         ws.on('open', () => {
           this._ws = ws;
           resolve();
diff --git a/lighthouse-core/gather/gatherers/dobetterweb/all-event-listeners.js b/lighthouse-core/gather/gatherers/dobetterweb/all-event-listeners.js
index 94b6a024f7d2..97c4cb99d01d 100644
--- a/lighthouse-core/gather/gatherers/dobetterweb/all-event-listeners.js
+++ b/lighthouse-core/gather/gatherers/dobetterweb/all-event-listeners.js
@@ -112,13 +112,10 @@ class EventListeners extends Gatherer {
    *     listeners found across the elements.
    */
   collectListeners(nodes) {
-    return nodes.reduce((chain, node) => {
-      return chain.then(prevArr => {
-        // Call getEventListeners once for each node in the list.
-        return this.getEventListeners(node.element ? node.element.nodeId : node)
-            .then(result => prevArr.concat(result));
-      });
-    }, Promise.resolve([]));
+    // Gather event listeners from each node in parallel.
+    return Promise.all(nodes.map(node => {
+      return this.getEventListeners(node.element ? node.element.nodeId : node);
+    })).then(nestedListeners => [].concat(...nestedListeners));
   }
 
   beforePass(options) {