is-absolute-url

Check if a URL is absolute. A lightweight utility function that determines whether a given URL string contains a protocol scheme, following RFC 3986 standards with special handling for Windows file path edge cases.

Package Information

• Package Name: is-absolute-url
• Package Type: npm
• Language: JavaScript (ES modules)
• Installation: npm install is-absolute-url

Core Imports

import isAbsoluteUrl from 'is-absolute-url';

This package is ES module only and does not support CommonJS require().

Basic Usage

import isAbsoluteUrl from 'is-absolute-url';

// Absolute URLs (contain protocol scheme)
isAbsoluteUrl('https://sindresorhus.com/foo/bar');
//=> true

isAbsoluteUrl('http://example.com');
//=> true

isAbsoluteUrl('file://path/to/file');
//=> true

isAbsoluteUrl('mailto:someone@example.com');
//=> true

isAbsoluteUrl('data:text/plain;base64,SGVsbG8sIFdvcmxkIQ%3D%3D');
//=> true

// Case insensitive scheme matching
isAbsoluteUrl('httpS://example.com');
//=> true

// Relative URLs (no protocol scheme)
isAbsoluteUrl('//sindresorhus.com');
//=> false

isAbsoluteUrl('/foo/bar');
//=> false

isAbsoluteUrl('foo/bar');
//=> false

// Windows paths are handled as non-absolute
isAbsoluteUrl('c:\\Windows\\System32');
//=> false

// Invalid scheme characters
isAbsoluteUrl('ht,tp://example.com');
//=> false

Capabilities

URL Validation

Determines if a URL string is absolute by checking for a valid protocol scheme.

/**
 * Check if a URL is absolute
 * @param {string} url - The URL string to check
 * @returns {boolean} true if the URL is absolute, false otherwise
 * @throws {TypeError} if url parameter is not a string
 */
export default function isAbsoluteUrl(url) {}

Parameters:

• url (string): The URL string to validate

Returns:

• boolean: true if the URL contains a valid protocol scheme, false otherwise

Throws:

• TypeError: If the url parameter is not a string

Implementation Details:

• Uses RFC 3986 compliant regex pattern for scheme validation
• Scheme must start with a letter followed by letters, digits, +, -, or .
• Explicitly rejects Windows file paths (e.g., c:\) to avoid false positives
• Case-insensitive scheme matching

Supported URL Schemes: All RFC 3986 compliant schemes are supported, including but not limited to:

• http:// and https://
• file://
• mailto:
• data:
• ftp://
• ldap://
• Custom schemes following the RFC pattern

Edge Cases:

• Protocol-relative URLs (//example.com) return false
• Windows file paths (c:\, C:\Dev\) return false
• Invalid scheme characters (ht,tp://) return false
• Empty strings return false

Error Handling

The function validates input types and throws a descriptive error for non-string inputs:

try {
  isAbsoluteUrl(123);
} catch (error) {
  console.log(error.message);
  // "Expected a `string`, got `number`"
}