Write a function to parses out just the domain name and returns it as a string.

domainName.js

/**
  Write a function that when given a URL as a string, parses out just the domain name and returns it as a string. 
  
  For example:
  url = "http://github.com/carbonfive/raygun" -> domain name = "github"
  url = "http://www.zombie-bites.com"         -> domain name = "zombie-bites"
  url = "https://www.cnet.com"                -> domain name = cnet"
**/

function domainName(url) {
  //your code here
}

//Test case
const { assert } = require("chai");

describe("Sample test", () => {
  it("Should pass sample tests", () => {
    assert.equal(domainName("http://google.com"), "google");
    assert.equal(domainName("http://google.co.jp"), "google");
    assert.equal(domainName("www.xakep.ru"), "xakep");
    assert.equal(domainName("https://youtube.com"), "youtube");
  });
});