Introduction

When building APIs with Express.js, handling client input via URLs is fundamental. Two of the most commonly used mechanisms are:

• URL Parameters (Route Params)

• Query Strings (Query Params)

What URL Parameters Are?

URL parameters are parts of the URL path used to identify a specific resource.

Example:

Fetching details of a user with given id

/users/42

In Express:

app.get('/users/:id', (req, res) => {
  const userId = req.params.id;
  res.send(`User ID is ${userId}`);
});

What Query Parameters Are?

Query parameters are key-value pairs appended to the URL after a ?.

Example:

/users?age=25&city=Mumbai

Now we are asking users whose age is 25 and city is Mumbai. It's kind of filtering.

In Express:

app.get('/users', (req, res) => {
  const { age, city } = req.query;
  res.send(`Age: \({age}, City: \){city}`);
});

Query Parameters are not only used for Filtering but also sorting and pagination

Differences Between URL Params and Query Strings

Feature	URL Parameters	Query Parameters
Location	Part of URL path	After ? in URL
Purpose	Identify specific resource	Modify/filter data
Required	Usually required	Usually optional
Example	/users/10	/users?age=20
Express Access	req.params	req.query

When to use params vs query?

Use URL Parameters When:

• You are accessing a specific resource

• The value is mandatory

• It defines the identity of the resource

Example:

GET /users/123
GET /orders/987

Use Query Parameters When:

• You are filtering or modifying results

• The values are optional

• You are dealing with lists or searches

Example:

GET /users?age=25
GET /products?category=electronics&sort=price