feat: expose browser context id (#9134)

Closes #9132

docs/api/puppeteer.browsercontext.id.md

@@ -0,0 +1,13 @@
+---
+sidebar_label: BrowserContext.id
+---
+
+# BrowserContext.id property
+
+**Signature:**
+
+```typescript
+class BrowserContext {
+  get id(): string | undefined;
+}
+```

docs/api/puppeteer.browsercontext.md

@@ -37,6 +37,12 @@ await page.goto('https://example.com');
 await context.close();
 ```
 
+## Properties
+
+| Property                               | Modifiers             | Type                | Description |
+| -------------------------------------- | --------------------- | ------------------- | ----------- |
+| [id](./puppeteer.browsercontext.id.md) | <code>readonly</code> | string \| undefined |             |
+
 ## Methods
 
 | Method                                                                                        | Modifiers | Description                                                                                                         |

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

@@ -178,4 +178,8 @@ export class BrowserContext extends EventEmitter {
   close(): Promise<void> {
     throw new Error('Not implemented');
   }
+
+  get id(): string | undefined {
+    return undefined;
+  }
 }

packages/puppeteer-core/src/common/Browser.ts

@@ -596,6 +596,10 @@ export class CDPBrowserContext extends BrowserContext {
     this.#id = contextId;
   }
 
+  override get id(): string | undefined {
+    return this.#id;
+  }
+
   /**
    * An array of all active targets inside the browser context.
    */

test/src/browsercontext.spec.ts

@@ -227,4 +227,16 @@ describe('BrowserContext', function () {
     remoteBrowser.disconnect();
     await context.close();
   });
+
+  it('should provide a context id', async () => {
+    const {browser} = getTestState();
+
+    expect(browser.browserContexts().length).toBe(1);
+    expect(browser.browserContexts()[0]!.id).toBeUndefined();
+
+    const context = await browser.createIncognitoBrowserContext();
+    expect(browser.browserContexts().length).toBe(2);
+    expect(browser.browserContexts()[1]!.id).toBeDefined();
+    await context.close();
+  });
 });