feat(js): export buildContextOptions helper (#262)

Co-authored-by: 이민재 <19909783+honor2030@users.noreply.github.com>

js/src/index.ts

@@ -16,7 +16,7 @@
  */
 
 // Launch functions (Playwright API)
-export { launch, launchContext, launchPersistentContext, buildLaunchOptions, humanizeBrowser } from "./playwright.js";
+export { launch, launchContext, launchPersistentContext, buildLaunchOptions, buildContextOptions, humanizeBrowser } from "./playwright.js";
 
 // Binary management
 export { ensureBinary, clearCache, binaryInfo, checkForUpdate } from "./download.js";

js/src/playwright.ts

@@ -44,6 +44,26 @@ function filterStealthCtxOptions(ctx?: BrowserContextOptions): Partial<BrowserCo
   return rest;
 }
 
+/**
+ * Build Playwright BrowserContext options for CloakBrowser without launching a browser
+ * or creating a context.
+ *
+ * Useful when integrating CloakBrowser with an existing Playwright Browser while
+ * keeping the wrapper's stealth-safe defaults for `newContext()`.
+ */
+export function buildContextOptions(
+  options: LaunchContextOptions = {}
+): BrowserContextOptions {
+  return {
+    // contextOptions first — explicit wrapper fields below override it.
+    // filterStealthCtxOptions strips locale/timezoneId to prevent CDP detection.
+    ...filterStealthCtxOptions(options.contextOptions),
+    ...(options.userAgent ? { userAgent: options.userAgent } : {}),
+    viewport: options.viewport === undefined ? DEFAULT_VIEWPORT : options.viewport,
+    ...(options.colorScheme ? { colorScheme: options.colorScheme } : {}),
+  } as BrowserContextOptions;
+}
+
 /**
  * Build Playwright launch options for CloakBrowser without starting Chromium.
  *
@@ -144,14 +164,7 @@ export async function launchContext(
 
   let context: BrowserContext;
   try {
-    context = await browser.newContext({
-      // contextOptions first — explicit wrapper fields below override it.
-      // filterStealthCtxOptions strips locale/timezoneId to prevent CDP detection.
-      ...filterStealthCtxOptions(options.contextOptions),
-      ...(options.userAgent ? { userAgent: options.userAgent } : {}),
-      viewport: options.viewport === undefined ? DEFAULT_VIEWPORT : options.viewport,
-      ...(options.colorScheme ? { colorScheme: options.colorScheme } : {}),
-    });
+    context = await browser.newContext(buildContextOptions(options));
   } catch (err) {
     await browser.close();
     throw err;
@@ -222,12 +235,7 @@ export async function launchPersistentContext(
     args,
     ignoreDefaultArgs: IGNORE_DEFAULT_ARGS,
     ...(proxyOption ? { proxy: proxyOption } : {}),
-    // contextOptions before explicit wrapper fields so explicit wins.
-    // filterStealthCtxOptions strips locale/timezoneId to prevent CDP detection.
-    ...filterStealthCtxOptions(options.contextOptions),
-    ...(options.userAgent ? { userAgent: options.userAgent } : {}),
-    viewport: options.viewport === undefined ? DEFAULT_VIEWPORT : options.viewport,
-    ...(options.colorScheme ? { colorScheme: options.colorScheme } : {}),
+    ...buildContextOptions(options),
     ...options.launchOptions,
   });
 

js/tests/launch.test.ts

@@ -40,13 +40,50 @@ describe("composable Playwright launch helpers", () => {
     }
   });
 
-  it("exports buildLaunchOptions and humanizeBrowser from the package entrypoint", async () => {
+  it("exports composable helpers from the package entrypoint", async () => {
     const entry = await import("../src/index.js");
 
     expect(entry.buildLaunchOptions).toBeTypeOf("function");
+    expect(entry.buildContextOptions).toBeTypeOf("function");
     expect(entry.humanizeBrowser).toBeTypeOf("function");
   });
 
+  it("buildContextOptions returns Playwright context options without launching a browser", async () => {
+    const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+    const { buildContextOptions } = await import("../src/index.js");
+
+    const options = buildContextOptions({
+      userAgent: "Explicit/1.0",
+      viewport: { width: 1280, height: 720 },
+      colorScheme: "dark",
+      contextOptions: {
+        userAgent: "Context/9.9",
+        viewport: { width: 9999, height: 9999 },
+        colorScheme: "light",
+        storageState: "state.json",
+        locale: "de-DE",
+        timezoneId: "Europe/Berlin",
+      },
+    });
+
+    expect(options).toMatchObject({
+      userAgent: "Explicit/1.0",
+      viewport: { width: 1280, height: 720 },
+      colorScheme: "dark",
+      storageState: "state.json",
+    });
+    expect(options.locale).toBeUndefined();
+    expect(options.timezoneId).toBeUndefined();
+    expect(warnSpy).toHaveBeenCalledTimes(2);
+  });
+
+  it("buildContextOptions applies DEFAULT_VIEWPORT by default and allows null viewport", async () => {
+    const { buildContextOptions } = await import("../src/index.js");
+
+    expect(buildContextOptions().viewport).toEqual(DEFAULT_VIEWPORT);
+    expect(buildContextOptions({ viewport: null }).viewport).toBeNull();
+  });
+
   it("buildLaunchOptions returns Playwright options without launching a browser", async () => {
     const freshConfig = await import("../src/config.js");
     vi.spyOn(freshConfig, "getPlatformTag").mockReturnValue("darwin-arm64");