JSFiddle - React, Tailwind, and code Playground

HTML

<p>
    Решение задачи не принимает мотивируя :
<br>
should not overwrite existing objects in the namespace
    Value is not what was expected <br>
should not replace the existing namespace object
    Value is not what was expected</p>

JavaScript

var MyNamespace = {}
MyNamespace.MyClass = function(param) {
  if(typeof param === 'string'){
        this.sayHello = function (){
          return param;
        }   
    }
 }
var myObject = new MyNamespace.MyClass('Hello');
var phrase = myObject.sayHello();