Problem: Build a Multi-Tenant Service Factory

hard

40 min

Create a factory that dynamically selects a service implementation based on tenant ID and service name.

Tenants may override zero, some, or all services. If a service is not defined for a tenant, it must fall back to the default implementation.

Goal

Implement createService(tenantId, serviceName) that returns the correct class instance—tenant-specific if defined, or default otherwise.

Constraints

Do not use if, switch, or ternaries to select or fall back between services.
Use object lookup and fallback chaining to resolve tenant-specific or default services.
Only instantiate the service inside the factory.
Consumers should not need to reference the "default" tenant explicitly—the factory must handle fallback logic automatically when a service is missing.

Sample output

The examples below illustrate what the output should look like:

const acmeLogger = createService('acme', 'Logger');
// Should use AcmeLogger (tenant override)
console.log(acmeLogger.log('Bootstrapped'));
/* Expected output:
Acme log: Bootstrapped */
const acmeAuth = createService('acme', 'Auth');
// Should fall back to DefaultAuth (not overridden by acme)
console.log(acmeAuth.login('alice'));
/* Expected output:
Default login for alice */
const unknownTenantLogger = createService('nonexistent', 'Logger');
// Should fall back to DefaultLogger (tenant doesn't exist)
console.log(unknownTenantLogger.log('Init'));
/* Expected output:
Default log: Init */
const defaultAuth = createService('default', 'Auth');
// Should still work when explicitly using default tenant
console.log(defaultAuth.login('bob'));
/* Expected output:
Default login for bob */

Problem: Build a Multi-Tenant Service Factory

hard

40 min

Create a factory that dynamically selects a service implementation based on tenant ID and service name.

Tenants may override zero, some, or all services. If a service is not defined for a tenant, it must fall back to the default implementation.

Goal

Implement createService(tenantId, serviceName) that returns the correct class instance—tenant-specific if defined, or default otherwise.

Constraints

Do not use if, switch, or ternaries to select or fall back between services.
Use object lookup and fallback chaining to resolve tenant-specific or default services.
Only instantiate the service inside the factory.
Consumers should not need to reference the "default" tenant explicitly—the factory must handle fallback logic automatically when a service is missing.

Sample output

The examples below illustrate what the output should look like:

const acmeLogger = createService('acme', 'Logger');
// Should use AcmeLogger (tenant override)
console.log(acmeLogger.log('Bootstrapped'));
/* Expected output:
Acme log: Bootstrapped */
const acmeAuth = createService('acme', 'Auth');
// Should fall back to DefaultAuth (not overridden by acme)
console.log(acmeAuth.login('alice'));
/* Expected output:
Default login for alice */
const unknownTenantLogger = createService('nonexistent', 'Logger');
// Should fall back to DefaultLogger (tenant doesn't exist)
console.log(unknownTenantLogger.log('Init'));
/* Expected output:
Default log: Init */
const defaultAuth = createService('default', 'Auth');
// Should still work when explicitly using default tenant
console.log(defaultAuth.login('bob'));
/* Expected output:
Default login for bob */

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Node.js

// JavaScript boilerplate
const serviceRegistry = {
  acme: {
    Logger: class AcmeLogger {
      log(msg) {
        return `Acme log: ${msg}`;
      }
    }
  },
  default: {
    Logger: class DefaultLogger {
      log(msg) {
        return `Default log: ${msg}`;
      }
    },
    Auth: class DefaultAuth {
      login(user) {
        return `Default login for ${user}`;
      }
    }
  }
};
// Implement this
function createService(tenantId, serviceName) {
  // Return instance from tenant namespace or fall back to default
}
// Example usage
const acmeLogger = createService('acme', 'Logger');
// Should use AcmeLogger (tenant override)
console.log(acmeLogger.log('Bootstrapped'));
/* Expected output:
Acme log: Bootstrapped */
const acmeAuth = createService('acme', 'Auth');
// Should fall back to DefaultAuth (not overridden by acme)
console.log(acmeAuth.login('alice'));
/* Expected output:
Default login for alice */
const unknownTenantLogger = createService('nonexistent', 'Logger');
// Should fall back to DefaultLogger (tenant doesn't exist)
console.log(unknownTenantLogger.log('Init'));
/* Expected output:
Default log: Init */
const defaultAuth = createService('default', 'Auth');
// Should still work when explicitly using default tenant
console.log(defaultAuth.login('bob'));
/* Expected output:
Default login for bob */

Problem: Build a Multi-Tenant Service Factory

Problem statement

Goal

Constraints

Sample output

Problem: Build a Multi-Tenant Service Factory

Problem statement

Goal

Constraints

Sample output