# Upgrading WebKit

Bun uses [a fork](https://github.com/Jarred-Sumner/WebKit) of WebKit with a small number of changes.

It's important to periodically update WebKit for many reasons:

- Security
- Performance
- Compatibility
- …and many more.

To upgrade, first find the commit in **bun's WebKit fork** (not bun!) between when we last upgraded and now.

```bash
cd src/bun.js/WebKit # In the WebKit directory! not bun
git checkout $COMMIT
```

This is the main command to run:

```bash
git pull https://github.com/WebKit/WebKit.git main --no-rebase --allow-unrelated-histories -X theirs
```

Then, you will likely see some silly merge conflicts. Fix them and then run:

```bash
# You might have to run this multiple times.
rm -rf WebKitBuild

# Go to Bun's directory! Not WebKit.
cd ../../../../
make jsc-build-mac-compile
```

Make sure that JSC's CLI is able to load successfully. This verifies that the build is working.

You know this worked when it printed help options. If it complains about symbols, crashes, or anything else that looks wrong, something is wrong.

```bash
src/bun.js/WebKit/WebKitBuild/Release/bin/jsc --help
```

Then, clear out our bindings and regenerate the C++<>Zig headers:

```bash
make clean-bindings jsc-bindings-headers generate-builtins
```

Now update Bun's bindings wherever there are compiler errors:

```bash
# It will take awhile if you don't pass -j here
make jsc-bindings-mac -j10
```

This is the hard part. It might involve digging through WebKit's commit history to figure out what changed and why. Fortunately, WebKit contributors write great commit messages.