service-box

'service-box' is a service registry for doing IoC within JavaScript apps. It differs from other service-registries / service-locators / ioc-containers in that it allows services to be created asynchronously while depending on other services that might also be created asynchronously, yet allows apps to synchronously retrieve services for simplicity.

Registry Initialization

You create your service registry like this:

import ServiceBox from 'service-box';
const serviceBox = new ServiceBox();

Before your app starts, you register factories for all of the services you have like this:

import {serviceFactory} from 'service-box';
import LogService from './LogService.js';
serviceBox.register('log-service', serviceFactory(LogService));

or, if you want / need to create the service-factory manually, then like this:

import LogService from './LogService.js';

serviceBox.register('log-service', function logServiceFactory() {
	return Promise.resolve(new LogService());
});

A service-factory is just a function that returns a promise containing the actual service. We use promises because some services only become available for use after they've initialized themselves by connecting to a server. We use service factories so that services can be registered in any order, avoiding the need for apps to transitively register a service's dependencies before registering the service itself.

Service factories can indicate whether the service they provide is dependent on other services by setting the dependencies property on the service factory, for example:

import PermissionService from './PermissionService.js';

function permissionServiceFactory() {
	const userService = serviceBox.get('user-service');
	return fetch(`./permisions/{userService.getUserId()}`).then(function(userPerms) {
		return new PermissionService(userPerms);
	});
};
permissionServiceFactory.dependencies = ['user-service'];

serviceBox.register('permission-service', permissionServiceFactory);

If the permissions for a given user were available directly from the user service as userService.getUserPerms(), then PermissionService could have requested these within its constructor, and we could have used the serviceFactory wrapper again, like so:

import {serviceFactory} from 'service-box';
serviceBox.register('permission-service',
	serviceFactory(PermissionService, ['user-service']));

In-App Usage

Apps can ensure that the services they need are available using serviceBox.resolveAll() as follows:

serviceBox.resolveAll().then(function() {
	// do app stuff here...
});

or, if they want to start doing useful work without creating all of the services, or before all of the dependent services have been registered, they can instead use serviceBox.resolve(services), like so:

serviceBox.resolve(['log-service', 'permission-service']).then(function() {
	// do app stuff here...
});

As we saw earlier, services are retrieved synchronously using the serviceBox.get() method. If a service isn't currently available then an error is thrown, and the app will need to be modified so that it correctly resolves the service first.