JS Design (Anti?)Patterns: Singleton, see more at https://medium.com/p/f375865bef10

DESIGN_PATTERNS_singletonExample.js

const utils = {
  deepFreeze: obj => {
    Object.freeze(obj);

    Object.getOwnPropertyNames(obj).forEach(prop => {
      const isNotNullOrUndefined = () =>
        obj[prop] !== null || typeof obj[prop] !== "undefined";

      const hasOwnProperty = () => obj.hasOwnProperty(prop);

      const isNotFreeze = () => !Object.isFrozen(obj[prop]);

      const isFunctionOrObject = () =>
        typeof obj[prop] === "function" || typeof obj[prop] === "object";

      if (
        isNotNullOrUndefined() &&
        hasOwnProperty() &&
        isNotFreeze() &&
        isFunctionOrObject()
      ) {
        utils.deepFreeze(obj[prop]);
      }
    });

    return obj;
  },
};

class ConfigParamsSingleton {
  constructor() {
    if (ConfigParamsSingleton.instance) {
      return ConfigParamsSingleton.instance;
    }

    this.params = {
      device: "iPhone",
      useGPS: false,
      useAcelerometer: true,
      deviceUniqueID: Math.floor(Math.random() * 300),
    };

    ConfigParamsSingleton.instance = this;
    utils.deepFreeze(ConfigParamsSingleton.instance);

    return ConfigParamsSingleton.instance;
  }

  getInstance() {
    return this.constructor();
  }

  getParams() {
    return this.params;
  }
}

const testSingleton = new ConfigParamsSingleton();

testSingleton.params.device = "Android";
testSingleton.params = { other: { complety: { different: "structure" } } };

console.log(testSingleton.getParams());

const otherTestsingleton = new ConfigParamsSingleton();

console.log(otherTestsingleton.getParams());

console.log(testSingleton === otherTestsingleton);