Create a web server with Express(v4) and listening on port 3000

Question

How to create a web server with *Express*(v4) and listening on port 3000?

Accepted Answer

```javascript
var app = require('express')();
app.listen(3000);
```

Answer

```javascript
var app = require('express').createServer();
app.listen(3000);
```

Answer

```javascript
var server = require('express').listen(3000);
```

Answer

```javascript
var app = require('express').server();
app.listen(3000);
```

Question from the Node.js test