JSFiddle - React, Tailwind, and code Playground

JavaScript

//function below should be called "SiteProfile", not "Site"
function SiteProfile() {
    this.url = "";
    this.name = "";

    this.Site = function(_url) {
        this.url = _url;
        this.name = this.ExtractNameFromURL();
    };

    this.ExtractNameFromURL = function() {
        var firstDOT = this.url.indexOf(".");
        var secondDOT = this.url.indexOf(".", firstDOT + 1);
        var theName = "";
        for (var i = firstDOT + 1; i < secondDOT; i++) {
            theName += this.url[i];
        }
        return theName;
    };
}

//now instantiate like this instead.
var site = new SiteProfile();
site.Site("www.google.co.il");
document.write(site.name); // with the changes above, this will behave as expected