URL Parameters vs Query Strings in Express.js
When building APIs or web applications with Express.js, you often need to send information through URLs.
For example:
Which user profile should be opened?
Which product should be displayed?
Which search filters should be applied?
This information is commonly passed using:
URL Parameters
Query Strings
Beginners often confuse these two concepts because both appear inside URLs.
But they solve different problems.
In this blog, you’ll learn:
What URL parameters are
What query parameters are
Their differences
How to access them in Express
When to use each approach
Understanding URLs First
Before learning params and query strings, let’s understand a basic URL.
Example:
https://example.com/users/101?sort=asc
This URL contains:
Path information
Query information
URL Structure Breakdown
https://example.com/users/101?sort=asc
│ │
│ └── Query String
│
└── URL Parameter
Both help send data to the server.
But they have different purposes.
What Are URL Parameters?
URL parameters are values embedded directly inside the URL path.
They usually identify:
A specific resource
A specific item
Real-Life Analogy
Think of URL params like:
- A house number
Example:
House #101
The number uniquely identifies a house.
Similarly:
/users/101
identifies:
- User 101
Example URL Parameter
/users/101
Here:
101is a URL parameter
It identifies:
- Which user we want
Express Route Example
app.get("/users/:id", (req, res) => {
res.send(`User ID is ${req.params.id}`);
});
Understanding :id
The :id part means:
“This value is dynamic.”
Express captures the value from the URL.
Example Request
/users/101
Result
req.params.id
// 101
Accessing Params in Express
Express stores URL parameters inside:
req.params
Example
app.get("/products/:productId", (req, res) => {
console.log(req.params.productId);
});
If the URL is:
/products/55
then:
req.params.productId
// 55
What Are Query Parameters?
Query parameters are extra values added after a ? in the URL.
They usually modify or filter data.
Example Query String
/products?category=phones
Here:
category=phonesis a query parameter
Real-Life Analogy
Think of query strings like:
- Search filters in online shopping
Example:
Color = black
Price < 5000
Brand = Samsung
The main page stays the same:
/products
But filters change the results.
Query Parameters Usually Represent
Filters
Sorting
Pagination
Search terms
Optional settings
Accessing Query Strings in Express
Express stores query parameters inside:
req.query
Example
app.get("/products", (req, res) => {
console.log(req.query.category);
});
Request:
/products?category=phones
Result:
req.query.category
// phones
Multiple Query Parameters
Example:
/products?category=phones&sort=price
Now the query object becomes:
{
category: "phones",
sort: "price"
}
Params vs Query: Core Difference
This is the most important concept.
URL Parameters
Usually identify:
Which specific resource?
Example:
/users/101
Meaning:
- User with ID 101
Query Parameters
Usually modify:
How data should be returned?
Example:
/users?sort=asc
Meaning:
- Return users sorted ascending
Params vs Query Comparison Diagram
URL Params
/users/101
↑
Specific Resource
Query Params
/users?sort=asc
↑
Filter / Modifier
Side-by-Side Comparison
| Feature | URL Params | Query Params |
|---|---|---|
| Position | Inside URL path | After ? |
| Purpose | Identify resource | Filter or modify |
| Express Access | req.params |
req.query |
| Usually Required | Yes | Often optional |
User Profile Example
URL Parameter
/users/101
Meaning:
- Open profile of user 101
The ID is essential.
Search Filter Example
Query Parameter
/search?keyword=laptop
Meaning:
- Search for laptops
The keyword modifies results.
Practical Express Example
URL Params Example
app.get("/users/:id", (req, res) => {
res.send(`Viewing user ${req.params.id}`);
});
Request:
/users/42
Response:
Viewing user 42
Query Params Example
app.get("/search", (req, res) => {
res.send(`Searching for ${req.query.keyword}`);
});
Request:
/search?keyword=javascript
Response:
Searching for javascript
When to Use URL Params
Use params when:
- The value identifies something specific
Examples:
User ID
Product ID
Order ID
Blog post slug
Good Examples
/users/101
/products/55
/orders/999
When to Use Query Params
Use query strings when:
Filtering
Searching
Sorting
Pagination
Optional settings
Good Examples
/products?category=phones
/search?keyword=nodejs
/users?page=2
Common Beginner Confusion
“Can IDs Be Passed in Query Strings?”
Yes.
Example:
/users?id=101
This technically works.
But REST-style APIs usually prefer:
/users/101
because:
- It clearly identifies a specific resource
Easy Rule to Remember
URL Params
WHO or WHAT?
Query Params
HOW?
Full Example URL
/products/55?color=black&sort=price
Breakdown:
| Part | Meaning |
|---|---|
/products/55 |
Specific product |
color=black |
Filter |
sort=price |
Sort option |
Complete URL Visualization
/products/55?color=black&sort=price
│
└── URL Parameter
│
└── Query Parameters
Why This Matters in Backend Development
You’ll use params and query strings constantly in:
REST APIs
Express apps
Search systems
E-commerce websites
Dashboards
Understanding the difference helps you design cleaner APIs.
Practice Exercises
Exercise 1
Create a route:
/users/:id
Return the user ID.
Exercise 2
Create a route:
/search?keyword=phone
Return the search keyword.
Exercise 3
Try combining both:
/products/55?color=red
Understand:
Which part is param
Which part is query
Final Thoughts
URL parameters and query strings both help send information through URLs, but they serve different purposes.
The easiest way to remember them:
| Type | Purpose |
|---|---|
| URL Params | Identify resource |
| Query Params | Filter or modify results |
In Express:
req.paramshandles route valuesreq.queryhandles query strings
Once this distinction becomes clear, working with APIs and backend routes becomes much easier.