Node.js URL.format(urlObject) API

The URL.format(urlObject) is the inbuilt API provided by URL class, which takes an object or string and return a formatted string derived from that object or string.

Syntax:

const url.format(urlObject)

If the urlObject is not an object or string, then it will throw a TypeError.
Return value: It returns string derived from urlObject.

The urlObject can have the following fields or keys:

• protocol
• slashes
• auth
• hostname
• host

• port
• pathname
• search
• query
• hash

The formatting process is as follows:

1. Initially, an empty string (‘’ say result) is created and then following parameters are looked for in order.

2. urlObject.protocol: string

• If urlObject.protocol is a string it is appended to the result else if not undefined and not a string then Error is thrown.
• If urlObject.protocol do not end with ASCII colon ( : ) then, the literal ‘:’ is appended to the result.

3. urlObject.slashes: boolean

• If either of the following property is true, then literals ‘//’ are appended to the result:
  • urlObject.slashaes is true.
  • urlObject.protocol is http, https, ftp, gopher, or file, then slashes will be automatically true even if slashes is false.

4. urlObject.auth: string

• If the urlObject.auth is not undefined and urlObject.host or urlObject.hostname is also not undefined then auth is appended to the result with literal ‘@’ irrespective of whether the literal ‘@’ present or not at the end.

5. urlObject.host: string

• If urlObject.host is a string it is appended to the result else if not undefined and not a string then Error is thrown.
• If it is undefined then urlObject.hostname is considered.

6. urlObject.hostname: string

• If urlObject.hostname is a string it is appended to the result else if not undefined and not a string then Error is thrown.
• If both host and hostname are defined then host will be given considered.

7. urlObject.port: (number | string)

• If hostname is considered and urlObject.port is defined then literal ‘:’ will be appended to the result along with urlObject.port.

8. urlObject.pathname: string

• If urlObject.pathname is a string but not empty string and not starting with literal ‘/’, then literal ‘/’ is appended to the result.
• urlObject.pathname is appended to the result.
• Else UrlObject.pathname is not a string then Error is thrown.

9. urlObject.search: string

• If urlObject.search is a string but not empty string and not starting with literal ‘?’, then literal ‘?’ is appended to the result.
• urlObject.search is appended to the result.
• If urlObject.search is not a string then Error is thrown.

10. urlObject.query: Object

• If urlObject.query is an Object then literal ‘?’ is appended to the result along with output of calling the querystring module’s stringify() method passing the value of urlObject.query.
• If both urlObject.search and urlObject.query are defined then urlObject.search will only be considered.

11. urlObject.hash: string

• If urlObject.hash is a string but not empty string and not starting with literal ‘#’, then literal ‘#’ is appended to the result.
• urlObject.hash is appended to the result.
• Else urlObject.hash is not a string and is not undefined then Error is thrown.

12. Finally, the result is returned.

Example 1

/*
  node program to demonstrate the URL.format API.
*/

//importing the module 'url'
const url = require('url');

//creating and initializing urlObject
var urlObject={
        protocol: 'https',
        hostname: 'example.com',
        port: 1800,
        pathname: 'sample/path',
        query: {
                page: 1,
                format: 'json'
        },
        hash: 'first'
    }

//getting the derived URL from urlObject using the url.format function
var sampleUrl=url.format(urlObject);

//Display the returned value
console.log(sampleUrl.toString());

Output: https://example.com:1800/sample/path?page=1&format=json#first

Example 2

/*
  node program to demonstrate the URL.format API.
*/

//importing the module 'url'
const url = require('url');

//creating and initializing urlObject
var urlObject={
        protocol: 'prct',
        slashes: false,
        host: 'example.com',
        auth: 'abc',
        pathname: '/sample/path',
        search: 'something',
        hash: 'first'
    }

//getting the derived URL from urlObject using the url.format function
var sampleUrl=url.format(urlObject);

//Display the returned value
console.log(sampleUrl.toString());

Output: prct:abc@example.com/sample/path?something#first

NOTE: The above program will compile and run by using the node fileName.js command.

Reference:
https://nodejs.org/api/url.html#url_url_format_urlobject