What does 'extended' mean in express 4.0?

If extended is false, you can not post "nested object"

person[name] = 'cw'// Nested Object = { person: { name: cw } }

If extended is true, you can do whatever way that you like.

When extended property is set to true, the URL-encoded data will be parsed with the qs library.

On the contrary,

when extended property is set to false, the URL-encoded data will instead be parsed with the querystring library.

The differences between parsing with `qs library` vs `querystring library`

• qs library allows you to create a nested object from your query string.

  var qs = require("qs")var result = qs.parse("person[name]=bobby&person[age]=3")console.log(result) // { person: { name: 'bobby', age: '3' } }

  
  

• query-string library does not support creating a nested object from your query string.

  var queryString = require("query-string")var result = queryString.parse("person[name]=bobby&person[age]=3")console.log(result) // { 'person[age]': '3', 'person[name]': 'bobby' }

  
  

• qs library will not filter out '?' from the query string.

  var qs = require("qs")var result = qs.parse("?a=b")console.log(result) // { '?a': 'b' }

  
  

• query-string library will filter out '?' from the query string.

  var queryString = require("query-string")var result = queryString.parse("?a=b")console.log(result) // { a: 'b' }

app.use(bodyParser.urlencoded({ extended: true })) // for parsing application/x-www-form-urlencoded

For more information, you may refer to Leonid Beschastny's answer, and npm compare qs vs query-string.

From the Body-Parser docs:

A new body object containing the parsed data is populated on the request object after the middleware (i.e. req.body). This object will contain key-value pairs, where the value can be a string or array (when extended is false), or any type (when extended is true).

And

The extended option allows to choose between parsing the URL-encoded data with the querystring library (when false) or the qs library (when true). The "extended" syntax allows for rich objects and arrays to be encoded into the URL-encoded format, allowing for a JSON-like experience with URL-encoded. For more information, please see the qs library.

Basically extended allows you to parse full objects.

Body Parser: Url Encoded