JSFiddle - React, Tailwind, and code Playground

HTML

<h1 id="example">
0
</h1>

JavaScript

function myString(string) {

  //Initalization function
  this.init = function() {
    this.calcLength();
  }

  // Storing the length of the string.
  this.length = 0;

  this.getLength = function() {
    return this.length;
  }

  // Calculates the length of a string
  this.calcLength = function() {
    for (var count in string) {
      this.length++;
    }
  };

  this.init();
}

// Implementation
var newStr = new myString("Hello");
var element = document.getElementById('example');
element.innertext = newStr.getLength();