From 4cce7e5bffa2e724bd8653b5487efb3b8d42ef64 Mon Sep 17 00:00:00 2001
From: Pavel Feldman <pavel.feldman@gmail.com>
Date: Tue, 26 Mar 2024 14:20:20 -0700
Subject: [PATCH] doc: document mocking read-only browser apis (#30122)

Documents https://github.com/microsoft/playwright/issues/30115
---
 docs/src/mock-browser-js.md | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/docs/src/mock-browser-js.md b/docs/src/mock-browser-js.md
index 26f76f6363..9647e0a151 100644
--- a/docs/src/mock-browser-js.md
+++ b/docs/src/mock-browser-js.md
@@ -60,6 +60,23 @@ test('show battery status', async ({ page }) => {
 
 ```
 
+## Mocking read-only APIs
+
+Some APIs are read-only so you won't be able to assign to a navigator property. For example,
+
+```js
+// Following line will have no effect.
+navigator.cookieEnabled = true;
+```
+
+However, if the property is [configurable](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty#configurable), you can still override it using the plain JavaScript:
+
+```js
+await page.addInitScript(() => {
+  Object.defineProperty(Object.getPrototypeOf(navigator), 'cookieEnabled', { value: false });
+});
+```
+
 ## Verifying API calls
 
 Sometimes it is useful to check if the page made all expected APIs calls. You can