From ddbf17aefb8169a225cefd691d519f218bcf217f Mon Sep 17 00:00:00 2001
From: EricHeitmuller-Gusto
 <153567695+EricHeitmuller-Gusto@users.noreply.github.com>
Date: Thu, 27 Jun 2024 23:10:39 -0700
Subject: [PATCH] Fix ResizeObserver initialization if document.body does not
 exist yet (close #1311)

PR #1322
---
 ...ore-document-body-ready_2024-06-27-05-58.json | 10 ++++++++++
 .../src/helpers/browser_props.ts                 |  3 +++
 .../test/browser_props.test.ts                   | 16 +++++++++++++++-
 3 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 common/changes/@snowplow/browser-tracker-core/issue-1311-reszieobserver-invoked-before-document-body-ready_2024-06-27-05-58.json

diff --git a/common/changes/@snowplow/browser-tracker-core/issue-1311-reszieobserver-invoked-before-document-body-ready_2024-06-27-05-58.json b/common/changes/@snowplow/browser-tracker-core/issue-1311-reszieobserver-invoked-before-document-body-ready_2024-06-27-05-58.json
new file mode 100644
index 000000000..af201dff9
--- /dev/null
+++ b/common/changes/@snowplow/browser-tracker-core/issue-1311-reszieobserver-invoked-before-document-body-ready_2024-06-27-05-58.json
@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@snowplow/browser-tracker-core",
+      "comment": "Fix ResizeObserver initialization if document.body does not exist yet (#1311)",
+      "type": "none"
+    }
+  ],
+  "packageName": "@snowplow/browser-tracker-core"
+}
\ No newline at end of file
diff --git a/libraries/browser-tracker-core/src/helpers/browser_props.ts b/libraries/browser-tracker-core/src/helpers/browser_props.ts
index 41250364a..4a247550d 100644
--- a/libraries/browser-tracker-core/src/helpers/browser_props.ts
+++ b/libraries/browser-tracker-core/src/helpers/browser_props.ts
@@ -22,6 +22,9 @@ function initializeResizeObserver() {
   if (resizeObserverInitialized) {
     return;
   }
+  if(!document || !document.body || !document.documentElement) {
+    return;
+  }
   resizeObserverInitialized = true;
 
   const resizeObserver = new ResizeObserver((entries) => {
diff --git a/libraries/browser-tracker-core/test/browser_props.test.ts b/libraries/browser-tracker-core/test/browser_props.test.ts
index 73a456e51..238c99ecb 100644
--- a/libraries/browser-tracker-core/test/browser_props.test.ts
+++ b/libraries/browser-tracker-core/test/browser_props.test.ts
@@ -1,4 +1,4 @@
-import { floorDimensionFields } from '../src/helpers/browser_props';
+import { floorDimensionFields, getBrowserProperties } from '../src/helpers/browser_props';
 
 describe('Browser props', () => {
   it('floorDimensionFields correctly floors dimension type values', () => {
@@ -10,4 +10,18 @@ describe('Browser props', () => {
     const testFractionalDimensions = '100.2x100.1';
     expect(floorDimensionFields(testFractionalDimensions)).toEqual('100x100');
   });
+
+  describe('#getBrowserProperties', () => {
+    describe('with undefined document', () => {
+      beforeAll(() => {
+        // @ts-expect-error
+        document = undefined;
+      });
+  
+      it('does not invoke the resize observer if the document is null', () => {
+        const browserProperties = getBrowserProperties();
+        expect(browserProperties).not.toEqual(null);
+      });
+    });
+  });
 });