With this, the user will be able to specify a `getId` function for their screens which returns an unique ID to use for the screen:
```js
<Stack.Screen
name="Profile"
component={ProfileScreen}
getId={({ params }) => params.userId}
/>
```
This is an alternative to the `key` option in `navigate` with several advantages:
- Often users specify a key that's dependent on data already in params, such as `userId`. So it's much easier to specify it one place rather than at every call site.
- Users won't need to deal with generating a unique key for routes manually.
- This will work with other actions such as `push`, and not just navigate.
- With this, it'll be possible to have multiple instances of the screen even if you use `navigate`, which may be desirable in many cases (such as profile screens).
BREAKING CHANGE: The lazy prop now can be configured per screen instead of for the whole navigator. To keep previous behavior, you can specify it in screenOptions
BREAKING CHANGE: Returning to first route after pressing back seems more common in apps. This commit changes the default for tab and drawer navigators to follow this common practice. To preserve previous behavior, you can pass backBehavior=history to tab and drawer navigators.
BREAKING CHANGE: This commit moves options from `drawerContentOptions` to regular `options` in order to reduce confusion between the two, as well as to make it more flexible to configure the drawer on a per screen basis.
BREAKING CHANGE: This commit moves options from `tabBarOptions` to regular `options` in order to reduce confusion between the two, as well as to make it more flexible to configure the tab bar based on a per screen basis.
BREAKING CHANGE: Previously, the stack header accepted scene and previous scene which contained things such as descriptor, navigation prop, progress etc. The commit simplifies them to pass `route`, `navigation`, `options` and `progress` directly to the header. Similaryly, the `previous` argument now contains `options`, `route` and `progress`.
BREAKING CHANGE: The header can be hidden with `headerShown: false` already. Using both `headerMode='none'` and `headerShown` together causes confusion. So it's time to drop the unnecessary `headerMode` prop.
BREAKING CHANGE: Previous versions of React Navigation merged params on navigation which caused confusion. This commit changes params not to be merged.
The old behaviour can still be achieved by passing `merge: true` explicitly:
```js
CommonActions.navigate({
name: 'bar',
params: { fruit: 'orange' },
merge: true,
})
```
`initialParams` specified for the screen are always merged.
BREAKING CHANGE: any code which relies on `route.state` will break.
Previous versions printed a warning on accessing `route.state`. This commit removes the property entirely. Accessing this property isn't safe since child navigator state isn't gurranteed to be in sync with parent navigator state and cause subtle bugs in apps.
