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param ​

Retrieves a route, query, file, or form parameter from the request context.

Syntax ​

js
const value = param('key')
const value = param('key', 'default')
const value = param('key', () => 'defaultFn')

Details ​

param attempts to retrieve a value from the following, in order:

  1. Route params
  2. Query string
  3. POST form data
  4. Uploaded files (if the key is associated with a file input)

If the key is not found in any source:

  • If a default value is provided, it is returned.
  • If a default function is provided, it is called and its return value is used instead.
  • Otherwise, undefined is returned.

Examples ​

Basic usage ​

js
// Route: /users/:id
// Request: GET /users/42
const id = param('id') // → '42'

With query string ​

js
// Request: GET /users?id=42&expand=true
const expand = param('expand') // → 'true'

With default fallback ​

js
const page = param('page', '1') // → '1' if not provided
const token = param('token', generateToken)

Retrieving uploaded file ​

js
const avatar = param('profile_picture')
if (avatar) {
  // avatar is available here and can be saved to database, etc.
  db.query("INSERT INTO avatars SET avt_image=?",avatar);
}

Notes ​

  • File parameters are available if the request is multipart/form-data.
  • In MARS Engine, param() unifies access across various request sources to simplify handler logic.