Explain the principle of the service locator pattern and its main features.

The Service Locator pattern is a way of organizing access to dependencies and services in an application through a centralized object (the locator). Instead of explicitly passing dependencies, components request the necessary services from the service locator.

Main features:

• Centralized management of dependencies.
• Simplifies component code, as they do not know how services are created.
• Ability to replace service implementations in one place.

However, the pattern is criticized for hiding dependencies, which complicates testing and understanding the code, as dependencies are implicit.

Example of usage:

class ServiceLocator {
  constructor() {
    this.services = new Map();
  }

  register(name, instance) {
    this.services.set(name, instance);
  }

  get(name) {
    return this.services.get(name);
  }
}

const locator = new ServiceLocator();
locator.register('logger', console);

const logger = locator.get('logger');
logger.log('Message');

In tests, services can be replaced with mocks by registering them in the locator.