Most developers running Playwright tests rely on Node.js. You install dependencies, start your test runner, and wait for results. That approach works, but it can be slow, especially as projects grow or tests multiply.
Even for small test suites, startup times and dependency resolution can add unnecessary delays. You spend minutes waiting before a single test actually runs, and it interrupts your workflow.
Bun addresses this directly. By combining JavaScript execution, package management, and fast test startup in one runtime, it makes your Playwright tests start faster, run more efficiently, and lets you focus on writing and debugging tests instead of waiting for them to execute.
Overview
What is Bun Playwright?
Bun Playwright is the setup where Playwright tests are executed using the Bun JavaScript runtime instead of Node.js, enabling faster test execution while retaining Playwright’s full cross-browser testing capabilities.
Key Aspects of Bun Playwright
- Playwright’s role: Handles browser automation across Chromium, Firefox, and WebKit with built-in test runners, assertions, and parallel testing.
- Bun’s role: Acts as the runtime that runs the test code, installs dependencies, and executes scripts with lower overhead.
- Why the combination matters: Running Playwright on Bun reduces startup and execution time, which is especially useful for large test suites and CI pipelines.
How Bun Playwright Works
- Bun setup: Bun is installed and used as the project’s JavaScript runtime instead of Node.js.
- Playwright installation: Playwright is added as a dependency using Bun’s package manager.
- Test configuration: Existing Playwright tests and configs remain largely unchanged, with scripts updated to run via Bun.
- Test execution: Bun launches the Playwright test runner, which controls browsers and executes test logic.
- Result handling: Playwright collects assertions, traces, and reports, while Bun’s faster execution reduces overall test runtime.
In this article, I will explain how to set up Bun for Playwright, configure it for your projects, and optimize test execution for speed and reliability.
What is Bun?
Bun is a modern JavaScript runtime that is faster and more efficient than Node.js. It is built with Zig, a low-level language focused on speed and minimal overhead. Bun executes JavaScript, TypeScript, and JSX natively.
Bun also includes a built-in bundler, transpiler, and package manager. This reduces the need for multiple separate tools. Projects start faster and require less setup compared to traditional Node.js environments.
For developers and testers, Bun provides a lean workflow for running scripts, managing dependencies, and automating tasks. This makes it a promising option for running end-to-end tests with Playwright more efficiently.
Can Playwright Work Natively with Bun?
Playwright does not have full native support for Bun. It is built for Node.js and relies on Node-specific APIs to launch and control browser processes. Bun’s runtime is not fully compatible with these APIs, which can cause issues with browser launches and child process handling when running Playwright tests directly in Bun.
Some developers experiment with Bun’s Node compatibility features or custom flags, but results can be inconsistent. Certain advanced Playwright features, such as tracing or network interception, may not work reliably under Bun without extra configuration.
Currently, Node.js remains the primary runtime for Playwright. Bun can run some test scripts, but it is not officially supported and cannot guarantee full feature compatibility.
Why Run Playwright Tests Using Bun?
Bun offers performance and workflow improvements for Playwright testing, though it is not a full Node.js replacement. It can reduce test startup times and make dependency management more efficient.
- Faster Test Startup: Bun compiles JavaScript and TypeScript on the fly and loads modules more efficiently than Node.js. For example, a test suite that takes 10 seconds to initialize on Node may start in 5-6 seconds on Bun. This is especially valuable when running frequent local tests during development.
- Reduced Configuration Overhead: Bun comes with a built-in package manager and bundler. Test projects no longer require separate installation of tools like Webpack, Vite, or npm scripts for dependency resolution. This simplifies CI pipelines and local setup.
- Parallel Test Efficiency: Bun’s lower memory footprint can allow multiple Playwright test instances to run concurrently without overloading the system. Teams running large end-to-end suites may see fewer crashes and smoother parallel execution.
Read More: How to Run Playwright Tests in Parallel
- Direct TypeScript Execution: Bun executes TypeScript files natively, avoiding the need for ts-node or pre-compilation steps. This reduces errors from mismatched compilation targets and accelerates iteration cycles.
- Faster Dependency Resolution for Node Modules: Bun’s package manager caches and resolves modules differently, making repeated test runs faster because it avoids repeated disk lookups and redundant downloads.
- Good for Experimentation and Local Development: Developers can use Bun to quickly iterate on tests and try new features, benchmarking performance improvements before committing to Node.js for full reliability.
Setting Up Playwright in a Bun Project
Setting up Playwright in a Bun project involves a few clear steps. Since Playwright is built for Node.js, some adjustments may be needed to ensure compatibility.
Step 1: Initialize a Bun Project
Start by creating a new Bun project using the command:
bun init
This generates a bun.lockb file and a basic project structure. Bun will manage dependencies natively, eliminating the need for npm or Yarn.
Step 2: Install Playwright
Add Playwright to your project with:
bun add @playwright/test
Bun installs the package quickly and caches dependencies efficiently. Large test suites benefit from faster installation compared to Node.js.
Step 3: Adjust Node-Specific Configurations
Playwright relies on Node-specific APIs for some features, such as custom browser paths or tracing. Update configuration files or environment variables as needed to match Bun’s runtime behavior.
Step 4: Use TypeScript Directly
If your tests are written in TypeScript, Bun can run .ts files without additional compilation. This removes the need for ts-node or pre-building scripts, speeding up development.
Step 5: Ensure Browsers Are Installed
Make sure Playwright’s browser binaries are available. Run the equivalent of Node’s npx playwright install to download Chromium, Firefox, and WebKit binaries so tests can launch browsers correctly.
Also Read: Chrome vs Chromium: Core Differences
Step 6: Run a Test Script
Create a simple test file and execute it using:
bun test
Check that the browser launches correctly and that the test runs without errors. This ensures that the environment is ready for more complex test suites.
How to Run Playwright Tests Using Bun Commands
Running Playwright tests in a Bun project follows a simple sequence of commands once the setup is complete.
Step 1: Verify Test Script
Ensure you have at least one Playwright test file, for example example.spec.ts. The test should include basic browser interactions, such as navigating to a page and checking for an element.
Step 2: Use Bun to Execute Tests
Run the test using Bun’s test runner with the command:
bun test example.spec.ts
Bun will compile TypeScript on the fly and execute the test. The startup time is typically faster than Node.js because Bun handles module resolution more efficiently.
Step 3: Run Multiple Tests
To execute the entire test suite, use:
bun test
Bun will locate all test files and run them in sequence. Parallel execution depends on Bun’s concurrency handling and available system resources.
Step 4: Pass Environment Variables
If your tests require environment-specific data, you can pass variables inline:
ENV=staging bun test
This allows you to run tests against different configurations without modifying the code.
Step 5: Inspect Test Output
Bun shows test results directly in the terminal. You can check for failed steps, browser errors, and timing metrics. This immediate feedback helps during local development and debugging.
Read More: Playwright Test Report: Comprehensive Guide
Step 6: Integrate With CI/CD
To run Bun-powered Playwright tests in a CI/CD pipeline, include the bun test command in your build scripts. Ensure that all necessary browser binaries are installed and that the environment mimics local setup to avoid runtime errors.
Performance Considerations: Bun vs Node.js for Playwright
Bun and Node.js handle Playwright tests differently, and the performance difference comes from how each runtime loads scripts and manages dependencies.
Here is a table that highlights the core differences between Bun vs Node.js for Playwright testing.
| Aspect | Bun | Node.js | Notes |
| Startup Time | Faster | Slower | Bun compiles JS/TS on the fly and resolves modules efficiently. Test suites start in ~50% less time. |
| Test Execution Speed | Similar | Similar | Browser automation dominates runtime. Bun’s advantage is mainly pre-test startup. |
| Memory Usage | Lower | Higher | Bun has a smaller footprint, allowing more parallel tests without overloading the system. |
| Dependency Resolution | Faster caching & resolution | Standard npm/Yarn resolution | Bun avoids repeated disk lookups, speeding repeated test runs. |
| TypeScript Handling | Native execution | Requires ts-node or pre-compilation | Bun can run .ts files directly, reducing setup and iteration overhead. |
| Feature Reliability | Partial support | Full support | Node.js supports all Playwright features; Bun may require workarounds for tracing, network interception, and custom browser paths. |
| CI/CD Integration | Faster for small/medium suites | Stable for all suites | Bun reduces pipeline time, but Node.js ensures full compatibility for complex end-to-end tests. |
Troubleshooting Common Playwright Bun Issues
Running Playwright in Bun can cause some runtime quirks due to Node.js-specific dependencies. The most common issues and solutions include:
- Browser Fails to Launch: Playwright may not start Chromium, Firefox, or WebKit due to missing binaries. Install the browsers manually with npx playwright install and adjust paths if Bun cannot locate them.
- Node API Errors: Some Node-specific APIs, like fs.promises or child_process, can throw errors in Bun. Replace them with Bun-compatible alternatives or polyfills, using Bun.file for file operations where possible.
- Tracing or Network Interception Fails: Advanced features like tracing or network interception may not work in Bun. Limit these tests to Node.js or use environment flags carefully to improve compatibility.
Also Read: How to Handle Trace Viewer in Playwright?
- TypeScript Compilation Issues: TypeScript files may fail due to unresolved paths or Node-specific imports. Bun runs TypeScript natively, so verify import paths and pre-compile only if necessary.
- Test Output is Incomplete: Console logs or test results may not display fully when running under Bun. Use bun test and enable BUN_DEBUG for detailed test logs to troubleshoot output issues.
Read More: How to Download Console Logs From a Website
- CI/CD Integration Failures: Tests working locally may fail in CI due to missing binaries or runtime differences. Ensure the CI environment has Bun installed and mirrors the local setup for browsers and configurations.
Why is Real Browser Testing Still Required with Bun and Playwright?
Bun speeds up local test execution but cannot fully replicate real browser behavior. Differences in rendering, JavaScript execution, OS-specific behavior, and features like network interception or tracing mean that issues can appear only on actual browsers.
While Bun is useful for faster iteration, verifying cross-browser compatibility, performance, and complex workflows requires testing on real devices and browsers.
Tools like BrowserStack solve this by providing access to real browsers and mobile devices in the cloud, so Playwright tests run exactly as users experience them. Teams can test across multiple browsers and devices at the same time, validate workflows that rely on device hardware or network conditions, and identify rendering or performance issues.
Here are the core features of BrowserStack that enhance Playwright tests:
- Real Device Cloud: Validates UI rendering, JavaScript execution, and browser behavior that Bun cannot accurately simulate.
- Parallel Testing: Offsets Bun’s local speed gains by running Playwright tests across multiple browsers and devices simultaneously.
- Local Environment Testing: Allows Playwright tests to run against internal or staging apps without exposing them publicly, which is critical when Bun is used only locally.
- Test Reporting & Analytics: Provides clear failure diagnostics, screenshots, and logs when issues appear only on real browsers.
- Web Performance Testing: Measures real-world load times and responsiveness, which Bun-based local runs cannot reliably capture.
- Payment Workflows: Ensures checkout and payment flows behave correctly in real browsers where timing, redirects, and third-party scripts matter.
Conclusion
Bun improves the speed of local Playwright test execution by reducing startup overhead and simplifying dependency management. It is well suited for rapid iteration during development, but its partial Node.js compatibility limits reliability for full end-to-end validation.
BrowserStack addresses this gap by running Playwright tests on real browsers and devices, where rendering, performance, and complex workflows behave as they do for real users. This allows teams to keep Bun for fast local feedback while relying on BrowserStack for accurate, production-grade validation before release.
