SPFxServicesConfiguration.ts

public onInit(): Promise<any> {
	return (
		super
		.onInit()
		// Set the global configuration of the application
		// This is where we will define the proper services according to the context (Local, Test, Prod,...)
		// or according to specific settings
		.then(() => {
	let scope = this.context.serviceScope;
				return new Promise((resolve, reject) => {
					if (this.properties.config) {
						switch (this.properties.config) {
							case 'config2':
								let childScope = scope.startNewChild();
								childScope.createAndProvide(GreetingsServiceKey, AltGreetingsService);
								childScope.finish();
								usedScope = childScope;
								break;
							case 'config1':
							default:
								break;
						}
					}

					scope.whenFinished(() => {
						resolve();
					});
			});
		})
	);
	}