# Migrating from V3
BlueRain V4 is a complete rewrite of the whole framework. These have resulted in some major breaking changes. We made a conscious decision to go ahead with it since we a major version, we wanted to do what's right, rather than carry mistakes of previous version.
This page should serve as a guide to migrate BlueRain projects from V3.
## New Version, New Name
The project name has changed in V4. Previous the framework was called `BlueRain OS`. We have decided to drop the `OS` part. So now, it's just `BlueRain`.
From V4 onwards, the project will move to it's new homes at:
* [Github](https://github.com/BlueEastCode/bluerain)
* [NPM](https://www.npmjs.com/package/@blueeast/bluerain)
Unfortunately, this also means that all import statements need to be migrated as well.
```diff
- import { BlueRain } from '@blueeast/bluerain-os';
+ import { BlueRain } from '@blueeast/bluerain';
```
## Bye Bye, withBlueRain
Theres no easy way to say this but... `withBlueRain` HOC is gone! Use `BlueRainConsumer` component instead.
We did this to simplify the API and to keep the bundle size in check.
```diff
- const Button = withBlueRain(({ BR, ...rest }) => {
- return ;
- });
+ const Button = (props) => (
+
+ {(BR) => }
+
+ );
```
## No Singleton Instance
In V3 we used a single instance of BlueRain. This instance was exported from the library as `default` and `BR`. This has been removed in the V4. This means:
* Now there is not default export in BlueRain 4.
* Now there is no single BlueRain instance exported.
This also allows us to use more than one BlueRain apps in a single project.
## Hooks
### Registry methods
Since registry codebase has been completely revamped, the internal API and methods has changed. So, if you use any of the `BR.Hooks` class methods directly, be sure to check docs for changes.
Some important changes are listed below:
#### Add/Remove methods
`add` and `remove` methods have been renamed to `register` and `unregister` respectively.
#### Set method
Behavior of set and remove has changed.
* `set` method sets the whole array of all listeners of a hook, as opposed to a single listener.
### Filter and Event Registries
Hooks in V3 were made of 2 registries:
* FilterRegistry
* EventRegistry
Both of these have been removed, and we only have a single unified registry now, i.e. HookRegistry.
This also means that there are no `BR.Filters` and `BR.Events` properties in BlueRain context anymore.
### Running a Hook
#### Return Type
All `BR.Hooks.run` now returns a [Promise](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise) that resolves a value, previously it just returned the value.
```diff
- modifier = BR.Hooks.run('movies.edit', modifier);
+ modifier = await BR.Hooks.run('movies.edit', modifier);
```
#### Arguments in handler function
In V3 a hook handler function could receive any number of arguments. This has been changed and now a hook can only receive 3 fixed arguments.
```diff
- BR.Hooks.run('movies.edit', movie, actors, collections);
+ BR.Hooks.run('movies.edit', movie, { actors, collections });
```
More details of about the arguments passed to the [handler function](https://blueeast.gitbook.io/bluerain/key-concepts/hooks#handler-function) can be found here.
## Plugins
### Registry methods
Since registry codebase has been completely revamped, the internal API and methods has changed. So, if you use any of the `BR.Plugins` class methods directly, be sure to check docs for changes.
Some important changes are listed below:
#### Add/Remove methods
`add` and `remove` methods have been renamed to `register` and `unregister` respectively.
#### Set method
Behavior of set and remove has changed.
* `set` method sets the whole array of all listeners of a hook, as opposed to a single listener.
#### initializeAll method
`initializeAll` method has been removed. Use `bluerain.plugins.initialize.all` hook instead.
```diff
- BR.Plugins.initializeAll();
+ await BR.Hooks.run('bluerain.plugins.initialize.all', bootOptions);
```
#### registerMany method
`registerMany` method has been removed. Use `bluerain.plugins.register` hook instead.
```diff
- BR.Plugins.registerMany(plugins);
+ await BR.Hooks.run('bluerain.plugins.register', bootOptions);
```
## Components
### IconEnhanced
IconEnhanced Component has been renamed to `DynamicIcon`
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