Factory & Constructor Functions

What problem does this initialization pattern solve?

const createService = (() => {
  let instance;
  
  return (config) => {
    if (instance) {
      return Object.freeze({ ...instance });
    }
    
    instance = {
      apiKey: config.apiKey,
      endpoint: config.endpoint,
      request(url) {
        // Make API request
      }
    };
    
    return Object.freeze({ ...instance });
  };
})();

It prevents memory leaks
It makes the service faster
It combines singleton behavior with immutable instances
This pattern combines singleton-like behavior (maintaining a single internal instance) with immutability (using Object.freeze) while still allowing each consumer to get their own frozen copy of the service. This solves several problems: 1) Ensures consistent configuration across the application, 2) Prevents accidental modification of the service instance, 3) Allows consumers to safely modify their copy without affecting others, and 4) Maintains the benefits of singleton initialization.
It improves API request performance

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