EZ-IOC

EZ-IOC is yet another dependency-injection/inversion-of-control package. It is super simple to configure and use, extremely lightweight, has no dependencies and doesn't use experimental decorators. And TypeScript definition files are included.

Features

An IOC container is used to bind an instance of an object to an interface or an identifier. It also allows you to inject dependencies into object constructors. This lets you to easily change implementations depending on the circumstances. Which is especially helpful for using mocks in unit tests.

• Bind names or symbols to
  • Constructor functions
  • Factory functions
  • Singleton object instances
• Define constructor dependencies
  • Dependency injection in deep object hierarchies

Install

npm i ez-ioc

How to Use

1. Create your own, or use the default IOC container
2. Define your bindings in the container
3. Resolve your bindings to get instances of objects

Quick Example

Here is a simple Typescript example:

interface Animal{...}
class Lion implements Animal{...}
class Bear implements Animal{...}
interface Zoo{...}
class MyZoo implements Zoo {
    constructor(animal1: Animal, animal2: Animal) {...}
}

import iocContainer from "ez-ioc";

// Bind Lion class to Animal interface
iocContainer.bind("Animal", Lion)
    // Bind "Bear" to a single instance of Bear
    .bind("Bear", new Bear())
    // Bind MyZoo class to Zoo interface and pass in resolved Animals to the constructor
    .bind("Zoo", MyZoo, ["Animal", "Bear"]);

// Get a Zoo instance with a Lion and Bear
const zoo: Zoo = container.resolve("Zoo");

Documentation

This package contains one class: EzIocContainer.

Get a Container

You can either create a container or use the default one. The advantage of using the default is that you can access it anywhere.

import iocContainer from "ez-ioc";

or

const iocContainer = require("ez-ioc");

Or create your own:

import {EzIocContainer} from "ez-ioc";
const myContainer = new EzIocContainer();

Configuration

The constructor can take a configuration object change certain functionality.

By default if you try to resolve an identifier that doesn't exist in your container it will throw an error. To override that behavior pass in a config object with allowUnbound set to true. In that case it will return undefined rather than throw an error.

By default if you try to bind to an identifier that has already been bound it will throw an error. To override that behavior pass in a config object with allowRebind set to true.

const myContainer = new EzIocContainer({
    allowUnbound: true,
    allowRebind: true    
});

Define Bindings

There are a number of different bindings you can create.

• Bind to an instance of an object (singleton)
• Bind to a constructor function
• Bind to a factory function

In all cases you bind an identifier to an implementation. The identifier can be a string or a Symbol.

There are four bind methods:

• bind()
• bindFactory()
• bindLazy()
• bindFactoryLazy()

Bind to Singleton

The simplest bind is binding to an instance of an object. Use the bind() method for this.

iocContainer.bind("Bear", new Bear());

Every time "Bear" is resolved it will return the same object.

Bind to Constructor

To bind to a object/class constructor also use the bind() method. This will create a new instance every time you resolve it.

iocContainer.bind("Animal", Lion);

If the constructor takes other dependencies as parameters you can define those as a third parameter which is an array of identifiers. The container will resolve those dependencies and inject them into the constructor in the order listed. If those dependencies also have dependencies they will be resolved too, all the way down the object hierarchy.

class MyZoo implements Zoo {
    constructor(readonly ...animals: Animal[]) {}
}
iocContainer.bind("Zoo", Zoo, ["Animal", "Bear"]);

Bind to Factory Function

You may also bind a factory function. A factory function is a function that creates an object. It works almost identically to binding a constructor except it uses the bindFactory() method. Note that the list of dependencies is optional.

const func = (a1, a2) => ({ animals: [a1, a2] });
iocContainer.bindFactory("Zoo", func, ["Animal", "Bear"]);

In this case the factory function will be called with the objects that "Animal" and "Bear" resolve to.

Lazy Load Bindings

Sometimes you may have an instance of an object that you want to create bindings for but are not sure that they will be used. In that case you can use lazy load bindings to bind a constructor or factory function. The first time the binding is resolved an object instance will be created and cached. Subsequent resolves will then use the cached instance.

Just use the bindLazy or bindFactoryLazy methods which take the same parameters as their non-lazy counterparts.

iocContainer.bindLazy("Zoo", Zoo, ["Animal", "Bear"]);

const func = (a1, a2) => ({ animals: [a1, a2] });
iocContainer.bindFactoryLazy("Zoo", func, ["Animal", "Bear"]);

Remove a Binding

If you have the need to remove a binding use unbind.

iocContainer.unbind("Animal");

Resolve Bindings

Use the resolve() method to resolve bindings. It works the same no matter which kind of binding you've created.

const zoo: Zoo = iocContainer.resolve("Zoo");

Async Bindings

You may have to bind a factory function that does some async work. In that case you will need to add async to the function definition and await to return a promise.

iocContained.bindFactory("MyService", async () => await getMyService());

Then when you resolve it you can use await to resolve the promise.

const svc: MyService = await iocContainer.resolve("MyService");

Using Symbols

If desired you can use Symbols instead of strings for bind identifiers. You might even build a set of identifiers and use them throughout your code to make sure you don't make mistakes. Usually you would use your type's name for the symbol name.

const TYPES = {
    Animal: Symbol.for("Animal"),
    Zoo: Symbol.for("Zoo")
};

iocContainer.bind(TYPES.Animal, Lion);
const animal = iocContainer.resolve(TYPES.Animal);

More Examples

For more examples visit the GitHub repo and look at the /examples folder or unit tests in the /spec folder.

https://github.com/jodymgustafson/ez-ioc

Code Hard