Make any class singletone

inject.service.ts

interface InjectionInstanceInterface {
    [key: string]: any;
}

interface ClassRef<T> extends Function {
    new (...args: any[]): T;
}

class InjectService {
    private instances: InjectionInstanceInterface = {};

    instance<T>(classFn: ClassRef<T>): T {
        const name = classFn.name;

        if (!this.instances[name]) {
            this.instances[name] = new classFn();
        }

        return this.instances[name];
    }
}

export const Inject = new InjectService();


/*
Usage:
=======================================================

class ExampleClass {
  example() {
    console.log(`example class and example method`);
  }
}

const instance1 = Inject.instance(ExampleClass);
const instance2 = Inject.instance(ExampleClass);

console.log(instance1 === instance2); // true
*/