visual studio not inputting URL into browser after driver.get(URL) because 'URL must be a string'

I have input the code, following along the video, and i'm up to the point of 6:45 where the teacher types in "set URL=port..... node index.js" and when I do the same I get an new open chrome browser (which is good) but the URL isn't set and the error I get is listed below. While playing around to get this to work, I don't get the "URL must be a string" error but I do get a "[Error] Error: ECONNREFUSED connect ECONNREFUSED 127.0.0.1:51539". I am permanently stuck, please send help!

"WebDriverError: unknown error: 'url' must be a string"

This is the code that i'm using:

require('chromedriver'); const selenium = require('selenium-webdriver'); const By = selenium.By;

const driver = new selenium.Builder() .forBrowser("chrome") .build();

driver.get(URL);

const locators = { inviteeForm: By.id("registrar"), inviteeNameField: By.name("name") };

function addInvitee(name) {

driver.findElement(locators.inviteeNameField)
    .sendKeys(name);
driver.findElement(locators.inviteeForm).submit();

}

addInvitee("Kevin Yu"); addInvitee("Joe Schmo");

This is the error:

[ERROR] node : C:\users\kevin.yu\selenium-basics\node_modules\selenium-webdriver\lib\promise.js:2626 [ERROR] AT line:1 char:1 [ERROR] + node index.js [ERROR] + ~~~~~~~~~~~ [ERROR] +Category Info :Not Specified: (C:\users\kevin...promise.js:2626:String) [], RemoteException [ERROR] + FullyQualifiedErrorId: Native Command Error [ERROR] [ERROR] throw error; [ERROR] ^ [ERROR] [ERROR] WebdriverError: uknown error: 'url' must be a string [ERROR] (Session info: chrome=68.0.3440.106 [ERROR] (Driver info: chromedriver=2.28.455520 (cc17746adff54984afff480136733114c6v3704b), platform=Windows NT 10.0.17134 x64_64) [ERROR] at Object.checkLegacyResponse (C:\Users\kevin.yu\selenium-basics\node_modules\selenium-webdriver\lib\error.js:546:15) [ERROR] at parseHttpResponse (C:\users\kevin.yu...…) [ERROR] doSend.then.response (C:\users\kevin.yu.....) [ERROR] at process.)_tickCallback (internal/process/next_tick.js:68:7) [ERROR] From: Task: WebDriver.navigate().to(undefined)