URL Parameters vs Query Strings in Express.js

When we build APIs or web applications using Node.js and Express, URLs become an important part of how data moves between the client and the server. Two common concepts you will see in almost every backend project are URL parameters and query strings.

At first, both may look similar because they both send values through the URL. But in real-world development, they are used for different purposes. Understanding when to use each one makes your API cleaner and easier to understand.

Your reference explained this idea using a library example.
In this article, we will understand these concepts in a more practical way using different examples.

Understanding URL Structure

Take a look at this URL:

http://localhost:3000/products/25/reviews?page=2&sort=latest

This URL contains both route parameters and query strings.

Breakdown:

/products/25/reviews

This part is the route path.

25

This is a URL parameter because it identifies a specific product.

Now look at this part:

?page=2&sort=latest

These are query strings because they change how the data is returned.

The ? The symbol separates the main route from the query values.

What are URL Parameters?

URL parameters are values written directly inside the route path. They are mainly used to identify a specific resource.

For example:

/products/25

Here, 25 could represent the ID of a product.

Another example:

/students/102

This route refers to a particular student.

In Express.js, parameters are created using a colon :.

Example:

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

app.get("/students/:studentId", (req, res) => {
  res.send(req.params);
});

app.listen(3000);

If the user visits:

/students/102

The output will be:

{
  studentId: "102"
}

Express stores all route parameters inside:

req.params

Multiple URL Parameters

You can also use more than one parameter in the same route.

Example:

app.get("/courses/:courseId/lessons/:lessonId", (req, res) => {
  res.send(req.params);
});

Request:

/courses/12/lessons/5

Output:

{
  courseId: "12",
  lessonId: "5"
}

This is useful when one resource belongs to another resource.

What are Query Strings?

Query strings are optional values added after the ? symbol in a URL. They are mostly used for filtering, searching, sorting, or pagination.

Example:

/products?category=mobile

Here, we are requesting products, but only from the mobile category.

Another example:

/movies?year=2025&rating=8

This route asks for movies filtered by year and rating.

In Express.js, query strings are available inside:

req.query

Example:

app.get("/movies", (req, res) => {
  res.send(req.query);
});

Request:

/movies?year=2025&rating=8

Output:

{
  year: "2025",
  rating: "8"
}

Important Point About Query Values

Everything received from req.query is treated as a string.

Example:

app.get("/items", (req, res) => {
  const page = parseInt(req.query.page) || 1;

  res.send(`Current page: ${page}`);
});

Request:

/items?page=3

Output:

Current page: 3

Without parseInt(), the value would remain a string.

Difference Between Params and Query Strings

URL Parameters	Query Strings
Part of the route	Added after ?
Used for identification	Used for filtering or modifying
Usually required	Usually optional
Accessed with req.params	Accessed with req.query
Helps find a specific resource	Helps customize results

When Should You Use URL Parameters?

Use URL parameters when the value is necessary to identify something specific.

Example:

/orders/500

Without the order ID, the request does not make sense.

Express example:

app.get("/orders/:orderId", (req, res) => {
  res.send(`Order ID: ${req.params.orderId}`);
});

When Should You Use Query Strings?

Use query strings when the route can still work without the value.

Example:

/products?sort=price

Even without sorting, /products still works.

Another example:

/articles?tag=nodejs

This only filters articles by tag.

Express example:

app.get("/articles", (req, res) => {
  const tag = req.query.tag;

  res.send(`Filtering by tag: ${tag}`);
});

Combining Both Together

In real projects, both are often used in the same route.

Example:

app.get("/teachers/:teacherId/classes", (req, res) => {
  const teacherId = req.params.teacherId;
  const subject = req.query.subject;

  res.send({
    teacherId,
    subject
  });
});

Request:

/teachers/45/classes?subject=math

Output:

{
  teacherId: "45",
  subject: "math"
}

Here:

• teacherId identifies the teacher

• subject filters the classes

Common Mistakes

Many beginners place filters inside the route path.

Wrong:

/products/electronics

This looks like electronics is a product ID or product name.

Better:

/products?category=electronics

Another example:

Wrong:

/news/latest

Better:

/news?sort=latest

Final Thoughts

URL parameters and query strings are both important parts of Express.js routing. Even though they look similar, their purpose is different.

• URL parameters help identify a specific resource.

• Query strings help modify or filter data.

A simple way to remember:

• Params → Which item?

• Query → How should the result look?