ES6+ Constructor Pattern

/**
 * @class
 * @name App
 *
 * @description Instance the main application
 */
class App {
    /**
     * @constructor
     * @description create and return a App instance
     */
    constructor() {
        if (!App.instance) {
            this.datas = {} // examples d'utilisation
            this.userAgent = navigator.userAgent.toLowerCase() // examples d'utilisation
            this.version = 'v0.0.1 - name'
            App.instance = this
            this.init()
        }
        return App.instance
    }

    /**
     * @name init
     * @description init the App
     */
    init() {
        this.exampleMethod()
        this.exampleMethod2()
    }

    /**
     * @name exampleMethod
     * @description an example method
     */
    exampleMethod() {
        console.log('example method 1')
        // ...
    }

    /**
 * @name exampleMethod2
 * @description another example method
 */
    exampleMethod2() {
        console.log('example method 2')
        // ...
    }

}

window.addEventListener('DOMContentLoaded', () => {
  const instance = new App()
  Object.freeze(instance)
})