@aesop-fables/containr

@aesop-fables/containr

containr is a lightweight Inversion of Control framework for Typescript. It is based on concepts/apis from StructureMap and Microsoft's Dependency Injection tooling.

Installation

npm install @aesop-fables/containr

yarn add @aesop-fables/containr

Usage

By and large, you really only do two kinds of things with containr:

1. Configure the container by registering the what and how containr should build or find requested services based on a key.
2. Resolve object instances of a service or dependency built out with all of its dependencies.

Registration

There are a variety of registration functions on the ServiceCollection class that you can use to control:

1. How your value/class gets resolved
2. When it gets resolved

Note:
v0.3* of `containr` introduced a new/simplified registration model. The team comes from a .NET background and sadly we bring some of that with us into Typescript generics sometimes. We're learning :).

1. factory(key: string, value: ValueFactoryDelegate, scope: Scopes)

Use this approach when you want to register a function to create your value/class. If you need service resolution, the function you register will receive an instance of IServiceContainer.

services.factory<string>(key, (container) => value, Scopes.Transient)

2. singleton(key: string, value: T)

Use this approach when you want to register a value directly.

services.singleton<string>(key, 'Hello, World!');

3. array(key: string, value: ValueFactoryDelegate<T> | T)

Use this approach when you want to add to an array of dependencies. This is useful when a class is depending an array of policies, etc. This approach is typically paired with the @injectArray(key: string) decorator.

services.array<string>(key, item1);

4. arrayAutoResolve(key: string, type: Newable<T>)

Use this approach when you want to add to an array of dependencies and also make use of containr's auto resolution pipeline. This approach is typically paired with the @injectArray(key: string) decorator.

services.arrayAutoResolve<IPolicy>(key, MyPolicy);

5. autoResolve(key: string, type: Newable<T>)

Use this approach when you want to register a class and make use of containr's auto resolution pipeline.

services.autoResolve<ISomething>(key, Something);

Scopes

Scopes control the lifetime and any caching of your dependencies. containr supports three scopes:

1. Transient

This is the default scope. Using this scope means that the container will cache your value. Most importantly, this scope is maintained when creating child containers if the value has already been resolved.

2. Singleton

This is the most straight-forward scope. Using this scope means that the container will cache your resolved value. This scope is always maintained when creating child containers.

3. Unique

Using this scope means that every attempt to resolve the dependency will result in a fresh instance (of the top-most dependency being requested).

Core Concepts

Configuring dependencies

In containr, values are registered against unique keys (strings). When you request for the container to get a dependency, you use a key to refer to it. The resolution logic works like:

1. Delegate to the configured scope for managing lifecyle (i.e., transient, unique, singleton)
2. When the dependency is being resolved and a factory was specified, invoke the factory (the scope may cache the value)
3. Pass it along to containr's interceptor model.

The "Bootstrapping" Phase

The process of creating a container is known as the bootstrapping phase (or used as a verb to refer to the act of creating the container).

Auto Resolution

Due to limitations in Typescript's support for overloading, there are functions designed for registering dependencies to use auto-resolution (e.g., add, use).

Service Modules

Service modules are blocks of code that are used to modify a ServiceCollection. They're designed to be reused and shared across projects (exported from custom npm packages). While it can be argued that it overlaps with React's naming conventions for hooks, we've employed a use* naming convention for service modules (e.g., useMyApi).

Example

// CaseApi.ts
import { AxiosInstance } from 'axios';
import { AxiosKeys } from '@aesop-fables/containr-axios';
import { IErrorRelay, ErrorRelayKeys } from '@aesop-fables/containr-error-relay';
import { inject } from '@aesop-fables/containr';

export interface ViewCaseModel {
    id: string;
    title: string;
    // ....
}

export interface ICaseApi {
    getCaseById(id: string): Promise<ViewCaseModel | null>;
}

export class CaseApi implements ICaseApi {
    constructor(
        @inject(AxiosKeys.Axios) private readonly axios: AxiosInstance,
        @inject(ErrorRelayKeys.Relay) private readonly errorRelay: IErrorRelay,
    ) {}

    getCaseById(id: string): Promise<ViewCaseModel | null> {
        return this.errorRelay.execute<ViewCaseModel>('CaseApi', async () => {
            const { data } = await this.axios.get<ViewCaseModel>(`/cases/${id}`);
            return data;
        });
    }
}

// bootstrap.ts
import { createContainer, createServiceModule, Scopes } from '@aesop-fables/containr';
import { useAxios } from '@aesop-fables/containr-axios';
import { ICaseApi, CaseApi } from './CaseApi';
import CaseServiceKeys from './CaseServiceKeys';

const useCaseServices = createServiceModule('cases', (services) => {
    services.factory<ICaseApi>(CaseServiceKeys.Api, CaseApi, Scopes.Transient);
});

export default function() {
    return createContainer([
        useAxios,
        useCaseServices,
    ]);
}

// App.tsx
import React from 'react';
import bootstrap from './Bootstrap';
import { ServiceContainer } from '@aesop-fables/containr-react';

const container = bootstrap();
export const App: React.FC = () => {
    return (
        <ServiceContainer container={container}>
         // ...
        </ServiceContainer>
    );
};

// ViewCase.tsx
import React from 'react';
import { ICaseApi } from './CaseApi';
import { useService } from '@aesop-fables/containr-react';
import CaseServiceKeys from './CaseServiceKeys';

export ViewCase: React.FC = ({ route }) => {
    const { id } = route;
    const [isLoading, setIsLoading] = useState(true);
    const [caseModel, setCaseModel] = useState<ViewCaseModel | undefined>(undefined);
    const caseApi = useService<ICaseApi>(CaseServiceKeys.Api);
    // We're using our error-relay framework that connects to react
    // so errors are handled at a higher level
    
    useEffect(() => {
        (async () => {
            try {
                const model = await caseApi.getCaseById(id);
                if (model) {
                    setCaseModel(model);
                }
            } finally {
                setIsLoading(false);
            }
        })();
    }
    }, [id]);

    if (isLoading) {
        return <p>Loading...</p>;
    }

    if (!caseModel) {
        return <div />;
    }

    return <p>{caseModel.title}</p>;
};