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In Express JS, query parameters are used to pass data to the server as part of the URL. They are appended to the URL after a question mark (?) and are typically used to filter or specify data that needs to be retrieved. When there are more than two query parameters in a URL, you separate them using the ampersand (&) symbol.

Lets see an example where i return the number of users based on name, designation and city using query params.

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' },
    { id: 4, name: 'Ravi', designation: 'Developer', city: 'Hyderabad' },
    { id: 5, name: 'Kiran', designation: 'Technical Lead', city: 'Hyderabad' },
];

// Route to get all users
app.get('/api/v1_0/users', (req, res) => {
    let filteredUsers = mockUsers;

    const { name, designation, city } = req.query;

    if (name) {
        filteredUsers = filteredUsers.filter(user => user.name.toLowerCase().includes(name.toLowerCase()));
    }

    if (designation) {
        filteredUsers = filteredUsers.filter(user => user.designation.toLowerCase().includes(designation.toLowerCase()));
    }

    if (city) {
        filteredUsers = filteredUsers.filter(user => user.city.toLowerCase().includes(city.toLowerCase()));
    }

    res.send({ users: filteredUsers });
});


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

Lets see in browser with name, city and designation filters.

• name filter

• city filter

• designation filter