Req Params

This property is an object containing properties mapped to the [named route "parameters"](/{{ page.lang }}/guide/routing.html#route-parameters). For example, if you have the route /user/:name, then the "name" property is available as req.params.name. This object defaults to Object.create(null) when using string paths, but remains a standard object with a normal prototype when the path is defined with a regular expression.

// GET /user/tj
console.dir(req.params.name)
// => "tj"

Properties corresponding to wildcard parameters are arrays containing separate path segments split on /:

app.get('/files/*file', (req, res) => {
  console.dir(req.params.file)
  // GET /files/note.txt
  // => [ 'note.txt' ]
  // GET /files/images/image.png
  // => [ 'images', 'image.png' ]
})

When you use a regular expression for the route definition, capture groups are provided as integer keys using req.params[n], where n is the n^th capture group.

app.use(/^\/file\/(.*)$/, (req, res) => {
  // GET /file/javascripts/jquery.js
  console.dir(req.params[0])
  // => "javascripts/jquery.js"
})

Named capturing groups in regular expressions behave like named route parameters. For example the group from /^\/file\/(?<path>.*)$/ expression is available as req.params.path.

If you need to make changes to a key in req.params, use the [app.param](/{{ page.lang }}/5x/api.html#app.param) handler. Changes are applicable only to [parameters](/{{ page.lang }}/guide/routing.html#route-parameters) already defined in the route path.

Any changes made to the req.params object in a middleware or route handler will be reset.

{% include admonitions/note.html content="Express automatically decodes the values in req.params (using decodeURIComponent)." %}