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In Express JS, route parameters are used to capture values specified at certain positions in the URL. They are defined by placing a colon (:) before the parameter name in the route path.

Lets see an example where we fetch the user based on id.

import express from "express"

const app = express();

const PORT = process.env.PORT || 5000;


const mockUsers = [
    { id: 1, name: 'Praveen', designation: 'Technical Architect', city: 'Hyderabad' },
    { id: 2, name: 'Prasad', designation: 'Technical Lead', city: 'Bangalore' },
    { id: 3, name: 'Anusha', designation: 'Lead Developer', city: 'Chennai' },
];

// Route to get a single user by ID
app.get('/api/v1_0/users/:id', (req, res) => {
    const parsedId = parseInt(req.params.id);
    if (isNaN(parsedId)) res.status(400).send({ msg: "Bad Request. Invalid ID" });
    const findUser = mockUsers.find((user) => user.id === parsedId);
    if (!findUser) res.status(404).send({ msg: "ID Not Found" });
    res.send(findUser);
});

app.listen(PORT, () => console.log(`Running on Port ${PORT}`));

There are 3 scenarios here,

• Bad Request

• ID Not Found

• Success