Bun

Can you use Bun while your app still runs on Node.js?

Yes. Bun can install the packages in an existing JavaScript project while Node.js still runs the app. Running the app with Bun is a separate choice. Check the launch command and what your host runs before switching it.

Bun implements many Node.js features, and some APIs work only in part. Verify the dependencies and tests your app actually uses before choosing Bun as the runtime. A successful package install alone cannot tell you how the app will behave.

What should the build do when the lockfile is stale?

When a project commits bun.lock, bun ci can install the recorded versions and fail if the package requirements and lockfile disagree. The lockfile is the file that records the versions selected for the build.

Treat this as an install. It changes the project’s installed packages and can run project setup scripts. Keep the intended lockfile and Bun version with the build instructions. If you are changing package managers, review the new lock and test before replacing the old build setup.

What should you check on Windows?

The official native Windows build requires Windows 10 version 1809 or newer. Bun provides x64 and ARM64 downloads. If you have an older x64 computer, check its processor against Bun’s requirements too.

An installer that runs on your laptop tells you that the tool starts there. Check any scripts and packages that use operating-system features on the machine that will run the app. Bun is open source. Hosting the app can have its own costs.

How can you plan one change at a time?

On paper, sketch a fictional project whose host runs Node.js and whose build uses an npm lockfile. Choose the installer change you want to evaluate first.

1. 1
   Keep the launch command steady

   Write down the Node.js launch command as the part that stays fixed. Record the existing package manager and lockfile for comparison.
2. 2
   Write down what an install would need

   Write that the reviewed bun.lock records version 1 of a fictional package called demo-calendar. If the project now requires version 2, a locked build should stop. Decide who will review the changed requirement and new lock before the build runs again.
3. 3
   Plan a separate runtime check

   If you later consider a Bun runtime, check that the host supports it. Use a disposable copy with no real accounts, data or credentials, and compare the app’s behavior against the Node.js version. Keep this exercise on paper if you cannot confirm that setup.