extractHostname — GTM Variable Template for URL

VARIABLES › URL

extractHostname CORE URL

Direct (.tpl) Apply (.tpl)

Extracts the hostname from a URL (without port).

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When to Use This

URL Processing

Parse, build, decode, and manipulate URLs and query parameters.

Extraction

Pull specific values, segments, or patterns from complex data structures.

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Examples

Hostname without port

INPUT

URL: https://example.com:8080/page

OUTPUT

example.com

Full hostname with subdomain

INPUT

URL: https://www.subdomain.example.com/page

OUTPUT

www.subdomain.example.com

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GTM Configuration

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Read-only Preview

extractHostname

URL

💾 The URL to extract the hostname from.

Supported formats:
  ✓ String

Input Setup

Input Function (optional)

⚙️ Optional pre-processing function applied to the input before internal logic (e.g., convert object to string, normalize case). Internal transformations such as case handling will still apply afterward.

Result Handling

Output Function (optional)

⚙️ Optional function to apply to the result before returning it (e.g., str => str + ' €', val => val !== undefined for boolean conversion). Useful for chaining transformations on the output.

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Related Variables

Same category: URL

→ buildUrlFromParts → completeUrl → decodeUri → decodeUriComponent → encodeURIComponent → encodeUri → extractHash → extractHashParams → extractHost → extractOrigin → extractPasword → extractPathname → extractPort → extractProtocol → extractSearch → extractSearchParams → extractSegmentByIndex → extractUserName → hasFragment → hasParameterWithValue → hasQueryString → parseUrlComponents → stringToPath

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Under the Hood

📜 View Implementation Code

/**
 * Extracts the hostname from a given URL.
 *
 * @param {string} data.src - The URL to extract the hostname from.
 * @param {Function|string} [data.out] - Optional output handler: function to transform result or string with format.
 *
 * Direct-mode specific parameters:
 * @param {Function} [data.pre] - Optional pre-processor function to transform src before extracting.
 * 
 * @returns {string|undefined} The hostname from the URL, or undefined if the input is invalid.
 *
 * @framework ggLowCodeGTMKit
 */

const parseUrl = require('parseUrl');

const extractHostname = function(url) {
    const parsed = parseUrl(url);
    return parsed && parsed.hostname || undefined;
};

const safeFunction = fn => typeof fn === 'function' ? fn : x => x;
const out = safeFunction(data.out);

// ===============================================================================
// extractHostname - Direct mode
// ===============================================================================
const applyCast = (castFn, value) => safeFunction(castFn)(value);
const value = applyCast(data.pre, data.src);
return out(extractHostname(value));

// ===============================================================================
// extractHostname() – Apply Mode
// ===============================================================================
/*
return function(value) {
   return out(extractHostname(value));
};
*/

🧪 View Test Scenarios (5 tests)

✅ '[example] Hostname without port'
✅ URL without port - should extract hostname
✅ '[example] Full hostname with subdomain'
✅ URL with query, hash and port - should extract hostname only
✅ Invalid URL - should return undefined