fix: deprecate isIncognito (#11962)

docs/api/puppeteer.browsercontext.isincognito.md

@@ -4,6 +4,10 @@ sidebar_label: BrowserContext.isIncognito
 
 # BrowserContext.isIncognito() method
 
+> Warning: This API is now obsolete.
+>
+> In Chrome, the [default browser context](./puppeteer.browser.defaultbrowsercontext.md) can also be "icognito" if configured via the arguments and in such cases this getter returns wrong results (see https://github.com/puppeteer/puppeteer/issues/8836). Also, the term "incognito" is not applicable to other browsers. To migrate, check the [default browser context](./puppeteer.browser.defaultbrowsercontext.md) instead: in Chrome all non-default contexts are incognito, and the default context might be incognito if you provide the `--incognito` argument when launching the browser.
+
 Whether this [browser context](./puppeteer.browsercontext.md) is incognito.
 
 In Chrome, the [default browser context](./puppeteer.browser.defaultbrowsercontext.md) is the only non-incognito browser context.

packages/puppeteer-core/src/api/BrowserContext.ts

@@ -144,6 +144,17 @@ export abstract class BrowserContext extends EventEmitter<BrowserContextEvents>
    * In Chrome, the
    * {@link Browser.defaultBrowserContext | default browser context} is the only
    * non-incognito browser context.
+   *
+   * @deprecated In Chrome, the
+   * {@link Browser.defaultBrowserContext | default browser context} can also be
+   * "icognito" if configured via the arguments and in such cases this getter
+   * returns wrong results (see
+   * https://github.com/puppeteer/puppeteer/issues/8836). Also, the term
+   * "incognito" is not applicable to other browsers. To migrate, check the
+   * {@link Browser.defaultBrowserContext | default browser context} instead: in
+   * Chrome all non-default contexts are incognito, and the default context
+   * might be incognito if you provide the `--incognito` argument when launching
+   * the browser.
    */
   abstract isIncognito(): boolean;