common-injector

Heavily influenced by Angular and it's dependency injection.

Inspired by Angular and Indiv.

A lightweight inversion of control container for JavaScript & Node.js apps.

中文

Usage

1. Install

npm install --save common-injector

1. Config

If you are using typescript, common-injector requires TypeScript >= 2.0 and the experimentalDecorators, emitDecoratorMetadata, types and lib compilation options in your tsconfig.json file.

{
    "compilerOptions": {
        "target": "es5",
        "module": "commonjs",
        "moduleResolution": "node",
        "experimentalDecorators": true,
        "emitDecoratorMetadata": true
    }
}

If you are using javascript and webpack, common-injector requires @babel/plugin-proposal-decorators and @babel/plugin-proposal-class-properties to support decorators in javascript.

{
  loader: 'babel-loader',
  options: {
    presets: [
      '@babel/preset-env',
    ],
    plugins: [
      '@babel/plugin-syntax-dynamic-import',
      ['@babel/plugin-proposal-decorators', { legacy: true }],
      ['@babel/plugin-proposal-class-properties', { loose: true }],
      'dynamic-import-webpack',
    ],
  },
}

1. Declare dependencies by using the @Injectable

Use decorator @Injectable to declare a dependency. And all dependencies will be a singleton instance in it's injector.

type InjectOptions = {
  provide?: any;
  injector?: Injector;
};
function Injectable(injectOptions?: InjectOptions): (_constructor: Function) => any;

@Injectable will put a dependency into a defalut injector rootInjector as IOC container.

@Injectable will use the class itself as a default token in the IOC container.

@Injectable accepts a parameter injectOptions: { provide?: any; injector?: Injector; }.

You can create other container with an instance which extends Injector by injectOptions.injector, or set an injection token for this injectable provider by injectOptions.provide.

import { Injectable } from 'common-injector';
 
class TestServiceToken {
  public num: number;
}
 
@Injectable({ provide: TestServiceToken })
class TestService {
  public num: number = 3;
}

Now TestService has been in our default injector, and we should use TestServiceToken as a token in the IOC container。

we can use it as a dependency，and need to use TestServiceToken as a token to mark this dependency.

Because of using lazy initialization to initialize dependency, please pay attention to the order of dependency.

1. Inject dependencies into a class by using the @Inject

Use decorator @Inject to inject a dependency as property of a class.

type InjectOptions = {
  provide?: any;
  injector?: Injector;
};
function Inject(injectOptions?: InjectOptions): (_constructor: any, propertyName: string) => any;

@Inject will get a dependency from a defalut injector rootInjector.

@Inject accepts a parameter InjectOptions, so you can choose this dependency from which injector with injectOptions.injector and use injectOptions.provide to reset a dependency instead of type of property or use injectOptions.provide to declare which dependency need to be injected in javascript.

import { Injectable, Inject } from 'common-injector';
 
class TestServiceToken {
  public num: number;
}
 
@Injectable({ provide: TestServiceToken })
class TestService {
  public num: number = 3;
}
 
class App {
  @Inject() private testService: TestServiceToken;
}

Because @Inject will set value in __proto__ of Object, so we should not change value of the injected property.

1. Create another Injector as container

• new Injector()

We can use another Injector as container, and an instance will be a singleton only in it's injector. singleton singleton will be only in this Injector

For example, we will creat a injector otherInjector as container and TestService2 will be put in otherInjector as a a singleton instance.

import { Injectable, Inject, Injector } from 'common-injector';
 
const otherInjector = new Injector();
 
@Injectable(otherInjector)
class TestService2 {
  public num: number = 3;
}

If you want to inject some instances from other Injector, should use injectOptions.injector to declare this instance will be injected from other Injector.

class App {
  @Inject() private testService: TestServiceToken;
  @Inject({injector: otherInjector}) private testService2: TestService2;
}

• injector.fork()

v0.0.3

We can use public method fork:() => Injector of Injector's instance to create a child container.

import { rootInjector } from 'common-injector';
 
const otherInjector = rootInjector.fork();

When request a dependency, injector tries to satisfy that dependency with a provider registered in his own injector.

If this injector lacks the provider, it passes the request up to its parent's injector.

If that injector can't satisfy the request, it passes the request along to the next parent injector up the tree.

The request of dependency keeps bubbling up until other injector finds or not find.

import { rootInjector } from 'common-injector';
 
@Injectable()
class TestServiceToken {
  public num: number = 3;
}
 
const childInjector = rootInjector.fork();
 
class App {
  @Inject({injector: childInjector}) private testService: TestServiceToken;
}

1. Set a constanst in Injector

In addition to @Injectable, with the method setInstance from instance of Injector, we can also insert a constant into Injector directly。

const otherInjector = new Injector();
class ConstantValue {
  public aaa: number;
}
otherInjector.setInstance(ConstantValue, {aaa: 123});

class App {
  @Inject() private testService: TestServiceToken;
  @Inject({injector: otherInjector}) private testService2: TestService2;
  @Inject({injector: otherInjector}) private constantValue: ConstantValue;
}

1. Used in javascript

Because of using Reflect.getMetadata('design:type') to get the type of property, when we use javascript, this API will be disable.

So in javascript, injectOptions.provide can be used to declare which provide of dependency will be injected.

class App {
  @Inject({provide: TestServiceToken}) testService;
  @Inject({injector: otherInjector, provide: TestService2}) testService2;
}