SimpleLocator-Node

SimpleLocator is a lightweight and fast Service Locator library for js that took inspiration from Splat for Xamarin.

• No reflection
• No generated code
• No annotation
• Simple to setup, simple to use: just initialize its rules and you are ready to go!
• Ability to add and override rules at runtime
• Unit test friendly (see below 'Best practices')
• Basic and singleton registration

How to install

npm i simple-locator

Basic usage

Your interface

interface IWeapon {

}

Your concrete class

class Sword implements IWeapon {

}

Define the rule:

SimpleLocator.set("WEAPON", () => {
    return new Sword()
})

Retrieve the concrete class

concrete = SimpleLocator.get("WEAPON") as IWeapon

Singleton

In the same way, one can register a class to be a singleton:

SimpleLocator.setSingleton("WEAPON", () => {
    return new Sword()
})

In this way, SimpleLocator will always return the same instance of MySampleConcreteClass

Multiple Registration

If you register the same class more times, SimpleLocator will consider only the last one

SimpleLocator.set("WEAPON", () => {
    return new Gun()
})

SimpleLocator.set("WEAPON", () => {
    return new Sword()
})
expect(SimpleLocator.get("WEAPON")).toBeInstanceOf(Sword)

Best practices

Using SimpleLocator doesn't mean that it's hard to mock your dependencies: to have it working alongside unit tests, consider to write your classes something like this:

class MyClass {
    private weapon: Weapon | null;

    constructor(listProvider: Weapon | null = null) {
        this.weapon = listProvider;
        if(this.weapon == null) {
            this.weapon = SimpleLocator.get("WEAPON") as Weapon
        }
    }
}

Then, register the rules like this:

SimpleLocator.set("WEAPON", () => {
    return new Gun()
})

SimpleLocator.set("MY_CLASS", () => {
    return new MyClass(SimpleLocator.get("WEAPON"))
})

In this way, you can create MyClass by calling:

myClass = SimpleLocator.get("MY_CLASS")

While in the unit tests, you will create it like this:

myClass = new MyClass( new MyMockedDependency() )