feat: Allow customising appProperties with a function

[benjackwhite]

Problem

Customer request was basically asking to omit one of the properties we bundle by default. This is currently already possible but only by extending the PostHog class and overriding the property like this:

class CustomPostHog extends PostHog {
  getCommonEventProperties(): any {
    const properties = super.getCommonEventProperties()
    // Filter out or add more properties here

    delete properties.$device_name

    return properties
  }
}

We do provide an option which was intended for providing your own "native" app properties if you don't want to use the libraries we support via native-deps but this becomes a full override, meaning you have to build all the options yourself manually.

PostHog.initAsync("token", { customAppProperties: {
  $device_name: 'My own thing',
}})

Changes

Allow customAppProperties to be a function that takes the existing properties

PostHog.initAsync('token', {
  customAppProperties: (props) => ({
    ...props,
    $device_name: 'CUSTOM!',
  }),
})

which feels a lot more client-friendly that overriding the class.

Release info Sub-libraries affected

Bump level

• [ ] Major
• [ ] Minor
• [x] Patch

Libraries affected

• [ ] All of them
• [ ] posthog-web
• [ ] posthog-node
• [x] posthog-react-native

Changelog notes

• Added support for customising the default app properties by passing a function to options.customAppProperties

[neilkakkar]

Lovely, elegant, I like it!