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docs/api/utility-apis: links out to api reference

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Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
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Patrik Oldsberg
2021-09-12 12:19:24 +02:00
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@@ -12,25 +12,32 @@ however always be a need for plugins to communicate outside of its boundaries,
both with other plugins and the app itself.
Backstage provides two primary methods for plugins to communicate across their
boundaries in client-side code. The first one being the `createPlugin` API and
the registration hooks passed to the `register` method, and the second one being
Utility APIs. While the `createPlugin` API is focused on the initialization
plugins and the app, the Utility APIs provide ways for plugins to communicate
during their entire life cycle.
boundaries in client-side code. The first one being the
[createPlugin](../reference/core-plugin-api.createPlugin.md) API along with the
extensions that it can provide, and the second one being Utility APIs. While the
[createPlugin](../reference/core-plugin-api.createPlugin.md) API is focused on
the initialization plugins and the app, the Utility APIs provide ways for
plugins to communicate during their entire life cycle.
## Consuming APIs
Each Utility API is tied to an `ApiRef` instance, which is a global singleton
object without any additional state or functionality, its only purpose is to
reference Utility APIs. `ApiRef`s are created using `createApiRef`, which is
exported by `@backstage/core-plugin-api`. There are many
[predefined Utility APIs](../reference/utility-apis/README.md) defined in
`@backstage/core-plugin-api`, and they're all exported with a name of the
pattern `*ApiRef`, for example `errorApiRef`.
Each Utility API is tied to an [ApiRef](../reference/core-plugin-api.ApiRef.md)
instance, which is a global singleton object without any additional state or
functionality, its only purpose is to reference Utility APIs.
[ApiRef](../reference/core-plugin-api.ApiRef.md)s are created using
[createApiRef](../reference/core-plugin-api.createApiRef.md), which is exported
by [@backstage/core-plugin-api](../reference/core-plugin-api.md). There are also
many predefined Utility APIs in
[@backstage/core-plugin-api](../reference/core-plugin-api.md), and they're all
exported with a name of the pattern `*ApiRef`, for example
[errorApiRef](../reference/core-plugin-api.errorApiRef.md).
To access one of the Utility APIs inside a React component, use the `useApi`
hook exported by `@backstage/core-plugin-api`, or the `withApis` HOC if you
prefer class components. For example, the `ErrorApi` can be accessed like this:
To access one of the Utility APIs inside a React component, use the
[useApi](../reference/core-plugin-api.useApi.md) hook exported by
[@backstage/core-plugin-api](../reference/core-plugin-api.md), or the
[withApis](../reference/core-plugin-api.withApis.md) HOC if you prefer class
components. For example, the
[ErrorApi](../reference/core-plugin-api.ErrorApi.md) can be accessed like this:
```tsx
import React from 'react';
@@ -48,24 +55,31 @@ export const MyComponent = () => {
};
```
Note that there is no explicit type given for `ErrorApi`. This is because the
`errorApiRef` has the type embedded, and `useApi` is able to infer the type.
Note that there is no explicit type given for
[ErrorApi](../reference/core-plugin-api.ErrorApi.md). This is because the
[errorApiRef](../reference/core-plugin-api.errorApiRef.md) has the type
embedded, and [useApi](../reference/core-plugin-api.useApi.md) is able to infer
the type.
Also note that consuming Utility APIs is not limited to plugins, it can be done
from any component inside Backstage, including the ones in
`@backstage/core-plugin-api`. The only requirement is that they are beneath the
`AppProvider` in the react tree.
[@backstage/core-plugin-api](../reference/core-plugin-api.md). The only
requirement is that they are beneath the `AppProvider` in the react tree.
## Supplying APIs
### API Factories
APIs are registered in the form of `ApiFactories`, which encapsulate the process
of instantiating an API. It is a collection of three things: the `ApiRef` of the
API to instantiate, a list of all required dependencies, and a factory function
that returns a new API instance.
APIs are registered in the form of
[ApiFactories](../reference/core-plugin-api.ApiFactory.md), which encapsulate
the process of instantiating an API. It is a collection of three things: the
[ApiRef](../reference/core-plugin-api.ApiRef.md) of the API to instantiate, a
list of all required dependencies, and a factory function that returns a new API
instance.
For example, this is the default `ApiFactory` for the `ErrorApi`:
For example, this is the default
[ApiFactory](../reference/core-plugin-api.ApiFactory.md) for the
[ErrorApi](../reference/core-plugin-api.ErrorApi.md):
```ts
createApiFactory({
@@ -79,18 +93,25 @@ createApiFactory({
});
```
In this example the `errorApiRef` is our API, which encapsulates the `ErrorApi`
type. The `alertApiRef` is our single dependency, which we give the name
`alertApi`, and is then passed on to the factory function, which returns an
implementation of the `ErrorApi`.
In this example the [errorApiRef](../reference/core-plugin-api.errorApiRef.md)
is our API, which encapsulates the
[ErrorApi](../reference/core-plugin-api.ErrorApi.md) type. The
[alertApiRef](../reference/core-plugin-api.alertApiRef.md) is our single
dependency, which we give the name `alertApi`, and is then passed on to the
factory function, which returns an implementation of the
[ErrorApi](../reference/core-plugin-api.ErrorApi.md).
The `createApiFactory` function is a thin wrapper that enables TypeScript type
inference. You may notice that there are no type annotations in the above
example, and that is because we're able to infer all types from the `ApiRef`s.
TypeScript will make sure that the return value of the `factory` function
matches the type embedded in `api`'s `ApiRef`, in this case the `ErrorApi`. It
will also match the types between the `deps` and the parameters of the `factory`
function, again using the type embedded within the `ApiRef`s.
The [createApiFactory](../reference/core-plugin-api.createApiFactory.md)
function is a thin wrapper that enables TypeScript type inference. You may
notice that there are no type annotations in the above example, and that is
because we're able to infer all types from the
[ApiRef](../reference/core-plugin-api.ApiRef.md)s. TypeScript will make sure
that the return value of the `factory` function matches the type embedded in
`api`'s [ApiRef](../reference/core-plugin-api.ApiRef.md), in this case the
[ErrorApi](../reference/core-plugin-api.ErrorApi.md). It will also match the
types between the `deps` and the parameters of the `factory` function, again
using the type embedded within the
[ApiRef](../reference/core-plugin-api.ApiRef.md)s.
## Registering API Factories
@@ -102,24 +123,27 @@ app, and the app itself.
Starting with the Backstage core library, it provides implementations for all of
the core APIs. The core APIs are the ones exported by
`@backstage/core-plugin-api`, such as the `errorApiRef` and `configApiRef`. You
can find a full list of them [here](../reference/utility-apis/README.md).
[@backstage/core-plugin-api](../reference/core-plugin-api.md), such as the
[errorApiRef](../reference/core-plugin-api.errorApiRef.md) and
[configApiRef](../reference/core-plugin-api.configApiRef.md).
The core APIs are loaded for any app created with `createApp` from
`@backstage/core-plugin-api`, which means that there is no step that needs to be
taken to include these APIs in an app.
The core APIs are loaded for any app created with
[createApp](../reference/core-app-api.createApp.md) from
[@backstage/core-plugin-api](../reference/core-plugin-api.md), which means that
there is no step that needs to be taken to include these APIs in an app.
### Plugin APIs
In addition to the core APIs, plugins can define and export their own APIs.
While doing so they should usually also provide default implementations of their
own APIs, for example, the `catalog` plugin exports `catalogApiRef`, and also
supplies a default `ApiFactory` of that API using the `CatalogClient`. There is
one restriction to plugin-provided API Factories: plugins may not supply
factories for core APIs, trying to do so will cause the app to refuse to start.
supplies a default [ApiFactory](../reference/core-plugin-api.ApiFactory.md) of
that API using the `CatalogClient`. There is one restriction to plugin-provided
API Factories: plugins may not supply factories for core APIs, trying to do so
will cause the app to refuse to start.
Plugins supply their APIs through the `apis` option of `createPlugin`, for
example:
Plugins supply their APIs through the `apis` option of
[createPlugin](../reference/core-plugin-api.createPlugin.md), for example:
```ts
export const techdocsPlugin = createPlugin({
@@ -144,7 +168,8 @@ Lastly, the app itself is the final point where APIs can be added, and what has
the final say in what APIs will be loaded at runtime. The app may override the
factories for any of the core or plugin APIs, with the exception of the config,
app theme, and identity APIs. These are static APIs that are tied into the
`createApp` implementation, and therefore not possible to override.
[createApp](../reference/core-app-api.createApp.md) implementation, and
therefore not possible to override.
Overriding APIs is useful for apps that want to switch out behavior to tailor it
to their environment. In some cases plugins may also export multiple
@@ -206,16 +231,19 @@ const app = createApp({
```
Note that the above line will cause an error if `IgnoreErrorApi` does not fully
implement the `ErrorApi`, as it is checked by the type embedded in the
`errorApiRef` at compile time.
implement the [ErrorApi](../reference/core-plugin-api.ErrorApi.md), as it is
checked by the type embedded in the
[errorApiRef](../reference/core-plugin-api.errorApiRef.md) at compile time.
## Defining custom Utility APIs
Plugins are free to define their own Utility APIs. Simply define the TypeScript
interface for the API, and create an `ApiRef` using `createApiRef` exported from
`@backstage/core-plugin-api`. Also be sure to provide at least one
implementation of the API, and to declare a default factory for the API in
`createPlugin`.
interface for the API, and create an
[ApiRef](../reference/core-plugin-api.ApiRef.md) using
[createApiRef](../reference/core-plugin-api.createApiRef.md) exported from
[@backstage/core-plugin-api](../reference/core-plugin-api.md). Also be sure to
provide at least one implementation of the API, and to declare a default factory
for the API in [createPlugin](../reference/core-plugin-api.createPlugin.md).
Custom Utility APIs can be either public or private, which is up to the plugin
to choose. Private APIs do not expose an external API surface, and it's
@@ -226,15 +254,18 @@ plugin to override the API in the app. It is however important to maintain
backwards compatibility of public APIs, as you may otherwise break apps that are
using your plugin.
To make an API public, simply export the `ApiRef` of the API, and any associated
types. To make an API private, just avoid exporting the `ApiRef`, but still be
sure to supply a default factory to `createPlugin`.
To make an API public, simply export the
[ApiRef](../reference/core-plugin-api.ApiRef.md) of the API, and any associated
types. To make an API private, just avoid exporting the
[ApiRef](../reference/core-plugin-api.ApiRef.md), but still be sure to supply a
default factory to [createPlugin](../reference/core-plugin-api.createPlugin.md).
Private APIs are useful for plugins that want to depend on other APIs outside of
React components, but not have to expose an entire API surface to maintain. When
using private APIs, it is fine to use the `typeof` of an implementing class as
the type parameter passed to `createApiRef`, while public APIs should always
define a separate TypeScript interface type.
the type parameter passed to
[createApiRef](../reference/core-plugin-api.createApiRef.md), while public APIs
should always define a separate TypeScript interface type.
Plugins may depend on APIs from other plugins, both in React components and as
dependencies to API factories. Do however be sure to not cause circular
@@ -242,13 +273,14 @@ dependencies between plugins.
## Architecture
The `ApiRef` instances mentioned above provide a point of indirection between
consumers and producers of Utility APIs. It allows for plugins and components to
depend on APIs in a type-safe way, without having a direct reference to a
concrete implementation of the APIs. The Apps are also given a lot of
flexibility in what implementations to provide. As long as they adhere to the
contract established by an `ApiRef`, they are free to choose any implementation
they want.
The [ApiRef](../reference/core-plugin-api.ApiRef.md) instances mentioned above
provide a point of indirection between consumers and producers of Utility APIs.
It allows for plugins and components to depend on APIs in a type-safe way,
without having a direct reference to a concrete implementation of the APIs. The
Apps are also given a lot of flexibility in what implementations to provide. As
long as they adhere to the contract established by an
[ApiRef](../reference/core-plugin-api.ApiRef.md), they are free to choose any
implementation they want.
The figure below shows the relationship between
<span style="color: #82b366">different Apps</span>, that provide
@@ -271,14 +303,17 @@ directly tied to React.
The indirection provided by Utility APIs also makes it straightforward to test
components that depend on APIs, and to provide a standard common development
environment for plugins. A proper test wrapper with mocked API implementations
is not yet ready, but it will be provided as a part of `@backstage/test-utils`.
It will provide mocked variants of APIs, with additional methods for asserting a
component's interaction with the API.
is not yet ready, but it will be provided as a part of
[@backstage/test-utils](../reference/test-utils.md). It will provide mocked
variants of APIs, with additional methods for asserting a component's
interaction with the API.
The common development environment for plugins is included in
`@backstage/dev-utils`, where the exported `createDevApp` function creates an
[@backstage/dev-utils](../reference/dev-utils.md), where the exported
[createDevApp](../reference/dev-utils.createDevApp.md) function creates an
application with implementations for all core APIs already present. Contrary to
the method for wiring up Utility API implementations in an app created with
`createApp`, `createDevApp` uses automatic dependency injection. This is to make
it possible to replace any API implementation, and having that be reflected in
dependents of that API.
[createApp](../reference/core-app-api.createApp.md),
[createDevApp](../reference/dev-utils.createDevApp.md) uses automatic dependency
injection. This is to make it possible to replace any API implementation, and
having that be reflected in dependents of that API.