Dependency Injection for Typescript

Automatic, no decorators, dependency injection library for your Typescript project.

Key features

• No decorators - completely no decorators whatsoever!
• Transparent - no changes to your code
• Automatically finds suitable implementation for interfaces by name
• Automatically finds suitable class based on a parent class
• Autowires everything, just like in Symfony or Spring
• Works just as fine when compiled
• As a bonus - exposes class reflection data

Installation

To install, if you use npm:

npm install aero-di

If you use yarn:

yarn add aero-di

Usage

First, you want to generate reflection data for your code. There is an included command that will do that for you. It would be best to put it into package.json scripts section, like that:

"generate-reflection": "aero-di-generate --baseDir src",

This command will scan the src directory and save reflection data to reflectionData.ts in that directory.

Hint: Generation command offers more options, explained in a section below.

You can now run this command. If you use npm, use:

npm run generate-reflection

If you use yarn:

yarn generate-reflection

Hint: It would be best to regenerate reflection with every build, so run it along your build, before running the typescript compiler.

After running this command, reflection data is ready. This is a normal source file that you can import and use as well, just don't edit it!

Now, to create your dependency injection container, import the library:

import { AeroDI } from "aero-di";

Import your generated reflection data as well, this can look like that:

import { classesReflection } from "./reflection";

Now initialize the container

const di = new AeroDI(classesReflection);

And that's it! You can now get an instance of a class:

const myInstance = await di.getByClass(MyClass);

You can also get an instance for an interface:

const myInstance = await di.getByInterface<ServiceInterface>("ServiceInterface");

Reflection command detailed usage

Available options (shortcut provided in parentheses):

• --baseDir (-b) - base directory to recursively search for source files
• --outFile (-o) - default: reflectionData.ts - file name to save reflection data to - it will be stored in baseDir
• --includeGlob (-i) - default: **/*.ts - glob for matching files, only files passing this glob will be analyzed
• --excludeGlob (-e) - default: **/*.spec.ts - glob for excluding files, files matched by this glob will not be analyzed
• --verbose (-v) - default: false - if used, information about analysis process will be printed

The file that is generated is not intended to be changed, but feel free to use it!

Example usage:

aero-di-generate --baseDir=src --outFile=gen.ts --includeGlob="**/*.ts" --excludeGlob="**/*.spec.ts"
aero-di-generate -b=src

Advanced usage

Of course the library must be able to handle a really challenging DI situations.

Here is explained how to tackle most of them:

Reflection data

To work, reflection data is a must, and the mechanism to support it is completely new. It does not use reflect-metadata or design stuff, but uses Typescript compiler api to read your code base and save what it reads to a typescript file. This also allows you to use this code like any other source file.

You can get the reflection data for objects, classes and class names from the DI as well, which is more handy, but nothing prevents you from using the reflection file directly.

Reflection saved in the file is basically an array of objects with following interface:

  fqcn: string; // Fully qualified class name - path and name
  name: string; // Class name
  ctor: Promise<Constructor> | null; // Constructor for that the class - null if not public
  implementsInterfaces: string[]; // Interfaces implemented by the class
  extendsClass: string | null; // Parent of the class - null if not extending
  constructorParameters: ParameterData[]; // Array of constructor parameters, with name and type fields
  constructorVisibility: "public" | "protected" | "private"; // Constructor visibility
  isAbstract: boolean; // Is the class abstract or not

Using this you can, for example, create an instance of a class by name, which is useful, for example, when recreating events from the database

FQCN is also very useful to distinguish 2 different classes with the same name

Get the DI injected itself in a class

AeroDI will register itself in the container when initialized. This means that getting it's instance in a class is as simple as using it in the container:

public constructor(
  private readonly di: AeroDI
)

Register already existing instance into the DI

At times your will have an instance and want the DI to see it, this is very simple as well. If you want to register it via the class name, use the following:

di.registerInstance(myInstance);

If you want to register it for a particular type name (class, or interface), you can do this:

di.registerInstanceForTypeName("MyInstanceInterface", MyInstance)

Hint: Remember, if the class that you are registering is in the directory scanned by the reflection generator, this is not needed!

Read class reflection

You can get class reflection data using an instance, a string of the class name, or a parent class name:

const metadataByInstance = di.metadataProvider.getByInterface("MyInterface");
const metadataByClassName = di.metadataProvider.getByClassName("MyClass");
const metadataByParentClass = di.metadataProvider.getByParentClassNameWithRoot("MyBaseClass");

Get classes implementing an interface

You can get class reflection data of classes implementing an interface like that:

const metadatas = di.metadataProvider.getByInterface("MyInterface");

Get a class hierarchy tree, based on extends

You can get class reflection data of classes in a class hierarchy tree, based on extends like that:

const withRootClass = di.metadataProvider.getByParentClassNameWithRoot("MyBaseClass");
const withoutRootClass = di.metadataProvider.getByParentClassNameWithoutRoot("MyBaseClass");

Register a global parameter

You can set up a global parameter that will be always injected if a parameter name is the same in any class constructor

di.parameterResolver.registerValueForParameterName("hostname", "127.0.0.1");

Register a scoped parameter

You can also set up a parameter that works like the global one, but only for one class. You can do it by class name or class constructor

di.parameterResolver.registerValueForClassAndParameterName(MyInstance, "hostname", "127.0.0.1");
di.parameterResolver.registerValueForClassNameAndParameterName("MyInstance", "hostname", "127.0.0.1");

Create multiple containers

There is no problem with having multiple DI instances at the same time, like that:

const commonData = classesReflection.filter(
    c => !c.name.endsWith("Handler") && !c.name.endsWith("Service"))
const handlersData = classesReflection.filter(c => c.name.endsWith("Handler"))
const servicesData = classesReflection.filter(c => c.name.endsWith("Service"))

const handlersDI = new AeroDI([...commonData, ...handlersData]);
const servicesDI = new AeroDI([...commonData, ...servicesData]);

Parameter resolving precedence

Value for a parameter in a constructor is resolved in the following order:

• Check for a scoped parameter - if found then use it
• Check for a global parameter - if found then use it
• Check for classes implementing used interface - if found then autowire and use it
• Check for classes by type - if found then autowire and use it
• Check for classes by parent tree - if found then autowire and use it

If an instance for a class or interface was already initialized once it is cached and used again. Eager loading can be accomplished by wiring desired classes just after DI was initialized. Support for transient instances is planned in the future.