What does 'extended' mean in express 4.0?

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 query-string library.

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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' }
  

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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.

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.