# URL Parameters vs Query Strings in Express.js

# 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**

```plaintext
/users/42
```

### In Express:

```javascript
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:

```plaintext
/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:

```javascript
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:**

```plaintext
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:**

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