Junior — Middle

Can you explain what the Singleton pattern is and in which cases it is used?

sobes.tech AI

Answer from AI

The Singleton pattern guarantees that a class has only one instance and provides a global point of access to it.

In Node.js, Singleton is often implemented through the module system: when a module is first imported, an object is created, which is then cached and reused in subsequent imports.

Example of a simple Singleton in Node.js:

// logger.js
class Logger {
  constructor() {
    if (Logger.instance) {
      return Logger.instance;
    }
    this.logs = [];
    Logger.instance = this;
  }

  log(message) {
    this.logs.push(message);
    console.log(message);
  }
}

module.exports = new Logger();

Usage:

const logger1 = require('./logger');
const logger2 = require('./logger');

logger1.log('First message');
console.log(logger1 === logger2); // true

Singleton is useful when you need to control access to resources, such as databases, logging, or configuration, to avoid creating multiple instances and to ensure data consistency.

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