nodejs，express搭建服务器，浏览器can't get /

刚开始学nodejs

const express = require ( "express" );
const app = express( );
app.get(" /" , ( req,res) => {
res.send ( "Hello world! " );})

const port = process.env.PORT ||5000;
app.listen(port, ( ) => {
console.log ( Server running on port ${port} );})

运行结果及报错内容

求问怎么解决？明明跟着教学视频一步一步走的

.js文件，第三行
" /",这个引号里如果有空格的话把空格去掉，只留下/