Express.js - Route called twice because of CORS

I have the following Node.js code:

import express from 'express';
import cors from 'cors';

const app = express();

// Enable CORS
const origin = [];

origin.push(
/http:\/\/localhost:.*/,
/https:\/\/localhost:.*/,
/http:\/\/127\.0\.0\.1:.*/,
/https:\/\/127\.0\.0\.1:.*/
);

app.use(
cors({
origin,
credentials: true
})
);

app.put('/', (req, res, next) => {
console.log('PUT REQUEST');
res.status(200).json({});
});

app.listen(5000, () => {
console.log('Server is running on port 5000');
});


When I call the route from Angular:

constructor(private http: HttpClient) {
this.http.put('http://localhost:5000', {}).subscribe();
}


I get this in my Node.js console:

PUT REQUEST
PUT REQUEST


The route is called twice when CORS is enabled. It doesn't happen when CORS is disabled:

// const origin = [];

// origin.push(
// /http:\/\/localhost:.*/,
// /https:\/\/localhost:.*/,
// /http:\/\/127\.0\.0\.1:.*/,
// /https:\/\/127\.0\.0\.1:.*/
// );

// app.use(
// cors({
// origin,
// credentials: true
// })
// );


The output without CORS is:

PUT REQUEST


Does somebody have an explanation/solution?

Note: I also tried to call the route from a React front and it runs properly. It looks like an issue with CORS and Angular.

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