When i try to learn node js

apiRest.js

const express = require('express');
const app = express();

app.use(express.json());
app.use(express.urlencoded({extended: true}))

const bikes = [
    {id: 1, color: 'blue'},
    {id: 2, color: 'red'}
];

function varExists(variable) {
    if (typeof req.body.color === "undefined") return false;
    return true;
}

app.get('/api/bikes', (req, res) => {
    res.send(bikes)
})

    .get('/api/bikes/:id', (req, res) => {
        const bike = bikes.find(b => b.id === parseInt(req.params.id));
        res.send(bike);
    })

    .post('/api/bikes/', (req, res) => {
        if (varExists(req.body.color) || req.body.color.length < 3) return res.status(400).send('Color is required');
        const bike = {
            id: bikes.length + 1,
            color: req.body.color
        };
        bikes.push(bike);
        res.send(bike);
    })

    .put('/api/bikes/:id', (req, res) => {
        // Edit a bike
    })

    .delete('/api/bile/:id', (req, res) => {
        // Delete a bike
    });

const port = process.env.PORT || 3000;
app.listen(port, (req, res) => {
    console.log('Server start listener on port ' + port + '...');
});