Relative vs absolute URL resolution in Node.js - Quick Revision & Key Differences

Recall & Review

beginner

What is an absolute URL?

An absolute URL is a full web address that includes the protocol (like http:// or https://), domain name, and the full path to a resource. It points to the exact location on the internet.

beginner

What is a relative URL?

A relative URL points to a resource based on the current page's location. It does not include the domain or protocol, just the path relative to where you are.

intermediate

How does Node.js resolve a relative URL against a base URL?

Node.js uses the URL constructor to combine a relative URL with a base absolute URL, producing a full absolute URL by filling in missing parts from the base.

beginner

Example: What is the absolute URL of 'images/photo.jpg' if the base URL is 'https://example.com/gallery/'?

The absolute URL is 'https://example.com/gallery/images/photo.jpg'. The relative path is added to the base URL's path.

beginner

Why is understanding relative vs absolute URLs important in web development?

It helps in correctly linking resources like images, scripts, and pages. Using the right URL type ensures links work no matter where the site is hosted or moved.

Which of the following is an absolute URL?

A ../page

B /page

C page.html

D https://site.com/page

An absolute URL includes the protocol and domain, like 'https://site.com/page'.

In Node.js, which object helps resolve relative URLs against a base URL?

A Http

B Path

C URL

D Fs

The URL constructor in Node.js resolves relative URLs against a base URL.

If the base URL is 'https://example.com/folder/' and the relative URL is '../file.txt', what is the resolved absolute URL?

A https://example.com/file.txt

B https://example.com/folder/file.txt

C https://example.com/folder/../file.txt

D https://example.com/folder/../folder/file.txt

The '..' moves one folder up, so the file is at 'https://example.com/file.txt'.

Which URL type is best to use when linking to resources within the same website?

A Absolute URL

B Relative URL

C Both are equally good

D Neither

Relative URLs are easier to maintain within the same site and adapt if the domain changes.

What happens if you use an absolute URL in your code and the domain changes?

A Links break because they point to the old domain

B Links automatically update

C Links become relative

D Nothing changes

Absolute URLs hardcode the domain, so if it changes, links break unless updated.

Explain the difference between relative and absolute URLs and how Node.js resolves them.

Think about how a relative path is combined with a base full address.

Describe a real-life scenario where choosing between relative and absolute URLs matters in a web project.

Consider what happens if you move your website to a new address.

Practice

1. Which of the following is a correct description of a relative URL in Node.js?

easy

A. A URL that includes the protocol and domain name.

B. A URL that depends on a base URL to form a full address.

C. A URL that always starts with 'http://' or 'https://'.

D. A URL that cannot be resolved using the URL class.

Solution

1. Step 1: Understand relative URL meaning

   A relative URL does not include the full path and depends on a base URL to form a complete address.

2. Step 2: Compare options

   A URL that depends on a base URL to form a full address. correctly describes this. Options B and C describe absolute URLs. A URL that cannot be resolved using the URL class. is incorrect because Node.js URL class can resolve relative URLs with a base.

3. Final Answer:

   A URL that depends on a base URL to form a full address. -> Option B

4. Quick Check:

   Relative URL = depends on base URL [OK]

Hint: Relative URLs need a base URL to become complete [OK]

Common Mistakes:

• Confusing relative URLs with absolute URLs
• Thinking relative URLs include protocol
• Believing relative URLs cannot be resolved

2. Which of the following is the correct way to create a new URL object for a relative path '/images/photo.jpg' with base 'https://example.com/gallery/' in Node.js?

easy

A. new URL('/images/photo.jpg', 'https://example.com/gallery/')

B. new URL('https://example.com/gallery/' + '/images/photo.jpg')

C. new URL('images/photo.jpg')

D. new URL('https://example.com/gallery/images/photo.jpg')

Solution

1. Step 1: Understand URL constructor usage

   The URL constructor takes two arguments: the path and the base URL. For relative paths, the first argument is the relative path, and the second is the base.

2. Step 2: Check each option

   new URL('/images/photo.jpg', 'https://example.com/gallery/') correctly uses new URL(relativePath, baseURL). new URL('https://example.com/gallery/' + '/images/photo.jpg') concatenates strings but does not use the URL constructor properly. new URL('images/photo.jpg') misses the base URL. new URL('https://example.com/gallery/images/photo.jpg') uses an absolute URL, not relative.

3. Final Answer:

   new URL('/images/photo.jpg', 'https://example.com/gallery/') -> Option A

4. Quick Check:

   URL(relative, base) = correct syntax [OK]

Hint: Use new URL(relativePath, baseURL) for relative URLs [OK]

Common Mistakes:

• Concatenating strings instead of using URL constructor
• Omitting the base URL for relative paths
• Passing absolute URL as first argument when base is given

3. What will be the output of the following Node.js code?

const { URL } = require('url');
const base = 'https://example.com/folder/';
const relative = '../image.png';
const fullUrl = new URL(relative, base);
console.log(fullUrl.href);

medium

A. https://example.com/folder/../image.png

B. Error: Invalid URL

C. https://example.com/image.png

D. https://example.com/folder/image.png

Solution

1. Step 1: Understand relative path resolution

   The relative path '../image.png' means go one folder up from 'https://example.com/folder/' which leads to 'https://example.com/'.

2. Step 2: Resolve the full URL

   Combining base and relative path, the URL class normalizes the path to 'https://example.com/image.png'. https://example.com/image.png matches this.

3. Final Answer:

   https://example.com/image.png -> Option C

4. Quick Check:

   Relative '..' moves up one directory [OK]

Hint: Relative '..' moves up one folder in URL paths [OK]

Common Mistakes:

• Not normalizing '..' in URL paths
• Expecting '../' to stay in the URL string
• Confusing relative and absolute URL outputs

4. Identify the error in this Node.js code snippet that tries to resolve a relative URL:

const { URL } = require('url');
const base = 'https://example.com/path';
const relative = 'file.txt';
const url = new URL(relative, base);
console.log(url.href);

medium

A. Base URL is missing trailing slash, causing incorrect resolution.

B. Relative URL should start with a slash '/' to be valid.

C. URL constructor requires only one argument for relative URLs.

D. No error; code outputs 'https://example.com/path/file.txt' correctly.

Solution

1. Step 1: Check base URL format

   The base URL 'https://example.com/path' lacks a trailing slash, so it is treated as a file, not a folder.

2. Step 2: Understand URL resolution effect

   Appending 'file.txt' to a base treated as file replaces 'path' with 'file.txt', resulting in 'https://example.com/file.txt', not 'https://example.com/path/file.txt'.

3. Final Answer:

   Base URL is missing trailing slash, causing incorrect resolution. -> Option A

4. Quick Check:

   Base URL trailing slash affects relative URL resolution [OK]

Hint: Always add trailing slash to base URL if it's a folder [OK]

Common Mistakes:

• Omitting trailing slash on base URL
• Thinking relative URLs must start with '/'
• Passing wrong number of arguments to URL constructor

5. You want to combine a base URL 'https://example.com/api/v1/' with a relative URL '../../images/pic.jpg' in Node.js. What will be the resolved absolute URL?

hard

A. https://example.com/api/v1/images/pic.jpg

B. https://example.com/api/images/pic.jpg

C. https://example.com/api/v1/../../images/pic.jpg

D. https://example.com/images/pic.jpg

Solution

1. Step 1: Analyze relative path '../../images/pic.jpg'

   The '../../' means go up two folders from 'https://example.com/api/v1/'.

2. Step 2: Move up two levels from base URL

   Starting at 'https://example.com/api/v1/', going up one level is 'https://example.com/api/', and up another is 'https://example.com/'. Then append 'images/pic.jpg'.

3. Final Answer:

   https://example.com/images/pic.jpg -> Option D

4. Quick Check:

   Two '..' moves up two directories [OK]

Hint: Count '..' to move up folders in URL paths [OK]

Common Mistakes:

• Not moving up enough folders for multiple '..'
• Appending relative path without normalization
• Confusing base URL folder levels