What Are URL Parameters?

URL parameters are dynamic values inside the URL path.

They usually identify a specific resource.

Example

/users/15

Here:

15

is the URL parameter.

URL Structure Breakdown

flowchart LR
    A[/users/15]
    A --> B[/users = route]
    A --> C[15 = parameter]

Express Route Example

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

Accessing URL Parameters

Use:

req.params

Example

app.get("/products/:productId", (req, res) => {
  console.log(req.params);

  res.send(req.params.productId);
});

URL

/products/50

Output

50

What Are Query Strings?

Query strings are optional values added after ? in a URL.

They are usually used for:

• Filtering

• Sorting

• Searching

• Pagination

Example

/products?category=shoes&sort=price

URL Breakdown

flowchart LR
    A[/products] --> B[?category=shoes]
    B --> C[&sort=price]

Accessing Query Strings in Express

Use:

req.query

Example

app.get("/products", (req, res) => {
  console.log(req.query);

  res.send(req.query.category);
});

URL

/products?category=shoes

Output

shoes

Params vs Query Strings

Practical Examples

URL Parameters → Identifiers

User Profile

/users/25

25 identifies a specific user.

Blog Post

/posts/100

100 identifies a specific post.

Query Strings → Filters or Modifiers

Search

/search?q=laptop

Pagination

/products?page=2

Sorting

/products?sort=price

Params vs Query Visualization

flowchart TD
    A[/users/15] --> B[15 = Identifier]
    C[/products?category=shoes] --> D[category = Filter]

Using Multiple Query Parameters

/products?category=phones&sort=price&page=2

Express Example

app.get("/products", (req, res) => {
  const category = req.query.category;
  const sort = req.query.sort;

  res.send(`${category} - ${sort}`);
});

Output

phones - price

Using Multiple URL Parameters

app.get("/users/:userId/orders/:orderId", (req, res) => {
  res.json(req.params);
});

URL

/users/15/orders/200

Output

{
  "userId": "15",
  "orderId": "200"
}

When to Use Params vs Query

Common Beginner Mistake

Incorrect:

/users?id=15

when identifying a specific user.

Better:

/users/15

Real-World API Examples

Combined Example

/users/15/orders?status=completed

Meaning

Express Example

app.get("/users/:id/orders", (req, res) => {
  const userId = req.params.id;
  const status = req.query.status;

  res.send(`User: ${userId}, Status: ${status}`);
});

Key Takeaways

Final Notes

A simple rule:

• Params identify what

• Query strings modify how

Examples:

/products/10

Specific product.

/products?category=phones

Filtered product list.