what should be the default port in app.js?

[lzl124631x]

I'm using express. Which port should I specify in the app.js as the port number when using the custom script?

When using default deployment script (i.e. without specifying command in .deployment), I used this config:

let PORT = process.env.PORT || 80;
app.listen(PORT, () => console.log(`listening on port ${PORT}!`));

But when using custom script, this doesn't work. I got error:

remote: Error: listen EACCES 0.0.0.0:80

What should I do?
Context that might help.