[Starting with Angular version 8](https://blog.angular.io/a-plan-for-version-8-0-and-ivy-b3318dfc19f7) you can opt-in to the new [Angular Ivy compilation and rendering pipeline].
-`enableIvy` set to `true` in `src/tsconfig.app.json`.
-`"aot": true` added to your default build options.
-`postinstall` script for the [Angular Compatibility Compiler](#ngcc).
{@a updating}
## Updating an existing project to use Ivy
By configuring a few key files, you can also update your existing project(s) to use Ivy.
- Add the `allowEmptyCodegenFiles` (needed only before version 8 final) and `enableIvy` options in the `angularCompilerOptions` in your project's `src/tsconfig.app.json`:
```json
{
"compilerOptions": { ... },
"angularCompilerOptions": {
"enableIvy": true,
"allowEmptyCodegenFiles": true,
}
}
```
- Set the default build options for your project to always use AOT compilation if it isn't already:
```json
{
"projects": {
"my-existing-project": {
"architect": {
"build": {
"options": {
...
"aot": true,
}
}
}
}
}
}
```
- Add a `postinstall` script to the workspace `package.json` file to run the [Angular Compatibility Compiler](#ngcc):
```json
{
"scripts": {
...
"postinstall": "ivy-ngcc"
}
}
```
- Reinstall your `package.json` dependencies to run the newly added script:
```
npm install
```
## Switching back to the current compiler
To stop using the Ivy compiler you need to undo the steps taken when [updating to use Ivy](#updating).
- Set `enableIvy` to false in `src/tsconfig.app.json`, or remove it completely.
- Remove `"aot": true` from your default build options if you didn't have it there before.
- Remove the `postinstall` script.
- Delete and reinstall your node modules.
{@a ngcc}
## The Angular Compatibility Compiler
Your third party libraries also need to be compiled with Ivy for you to use them in your Ivy application.
That's where the Angular Compatibility (`ngcc`) compiler comes into play.
We set it as a postinstall script in your `package.json` so that it always runs when you install
your `package.json` dependencies.
Using a postinstall hook to run `ngcc` is just a temporary integration.
We expect `ngcc` to be seamlessly integrated into the Angular CLI build pipeline in the future before the full Ivy rollout.
Once that's implemented `ngcc` will not be visible to developers.
Until that happens, opting into Ivy means that all projects in a single CLI workspace will be compiled with Ivy.
Note: we are aware of build-time performance issues with ngcc. Please bear with us while we improve the tooling and build integration in the Angular CLI.
