javascript - Express not working as expected -

i trying set react app express running. however, can't understand why won't load page want to

this app.js:

var express = require('express'); var app = express();  app.use('/', express.static('public'));  app.get('/', function(req, res) {     res.sendfile('./index.html'); });  app.get('/canyouplay.js', function(req, res) {     res.sendfile('/canyouplay.html'); });  app.listen(process.env.port || 8080); 

this works. if change first app.get to:

app.get('/', function(req, res) {     res.sendfile('./canyouplay.html'); }); 

it still renders same html file when restarting app though different files.

also when run function:

  handleclick: function() {     document.location.replace('./canyouplay'); }, 

it says cannot /canyouplay though html , js file exist name.

what have missed or doing wrong?