From 22f2d6f292be9a5c4b8b52d973e20ac7b21f688d Mon Sep 17 00:00:00 2001
From: Luke Barnard <luke@matrix.org>
Date: Thu, 3 May 2018 14:08:10 +0100
Subject: [PATCH] Fix crash when browser doesn't report page change measurement

---
 src/Analytics.js                        | 9 ++++++---
 src/components/structures/MatrixChat.js | 4 ++++
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/Analytics.js b/src/Analytics.js
index 8b55bdfd64..0d1313f48d 100644
--- a/src/Analytics.js
+++ b/src/Analytics.js
@@ -164,9 +164,13 @@ class Analytics {
     }
 
     trackPageChange(generationTimeMs) {
-        if (typeof generationTimeMs !== 'number') {
-            throw new Error('Analytics.trackPageChange: expected generationTimeMs to be a number');
+        if (typeof generationTimeMs === 'number') {
+            this._paq.push(['setGenerationTimeMs', generationTimeMs]);
+        } else {
+            console.warn('Analytics.trackPageChange: expected generationTimeMs to be a number');
+            // But continue anyway because we still want to track the change
         }
+
         if (this.disabled) return;
         if (this.firstPage) {
             // De-duplicate first page
@@ -175,7 +179,6 @@ class Analytics {
             return;
         }
         this._paq.push(['setCustomUrl', getRedactedUrl()]);
-        this._paq.push(['setGenerationTimeMs', generationTimeMs]);
         this._paq.push(['trackPageView']);
     }
 
diff --git a/src/components/structures/MatrixChat.js b/src/components/structures/MatrixChat.js
index 8df46d2f7c..3005bc86ad 100644
--- a/src/components/structures/MatrixChat.js
+++ b/src/components/structures/MatrixChat.js
@@ -413,6 +413,10 @@ export default React.createClass({
         performance.clearMarks('riot_MatrixChat_page_change_start');
         performance.clearMarks('riot_MatrixChat_page_change_stop');
         const measurement = performance.getEntriesByName('riot_MatrixChat_page_change_delta').pop();
+
+        // In practice, sometimes the entries list is empty, so we get no measurement
+        if (!measurement) return null;
+
         return measurement.duration;
     },