JSFiddle - React, Tailwind, and code Playground

JavaScript

function Test() {

      var x = 100;

      this.number = function() {
        var x = 5;
        letsgo(); 
      }

      function letsgo() {
        document.write('x == ' + x);
      }

    }

    var test = new Test();

    test.number(); //100, не 5