GTM Variable Configuration

GTM Variable Configuration

Sources:

• https://support.google.com/tagmanager/topic/9125128
• https://developers.google.com/tag-platform/tag-manager/web

Last Updated: 2025-01-09

Overview

Variables in Google Tag Manager store and provide dynamic values for use in tags, triggers, and other variables. They capture information from the page, data layer, cookies, URLs, and more. This guide covers all variable types and configuration patterns.

Variable Fundamentals

How Variables Work

Variables capture values that can be:

• Used in tag configurations (e.g., event parameters)
• Used in trigger conditions (e.g., fire when X equals Y)
• Referenced by other variables
• Displayed in Preview mode for debugging

Variable Syntax

Reference variables using double curly braces:

{{Variable Name}}

Example in tag configuration:

Event Name: {{Event Name Variable}}
User ID: {{DL - User ID}}

Built-in Variables

Enabling Built-in Variables

1. Go to Variables
2. Click "Configure" in Built-in Variables section
3. Enable required variables

Page Variables

Click Variables

Form Variables

History Variables

Utility Variables

Video Variables

Scroll Variables

Visibility Variables

User-Defined Variables

Data Layer Variable

Access values from the data layer:

Variable Type: Data Layer Variable
Data Layer Variable Name: userId
Data Layer Version: Version 2

Accessing Nested Values:

Data Layer Variable Name: ecommerce.items.0.item_name

Data Layer Push:

dataLayer.push({
  'userId': 'USER123',
  'ecommerce': {
    'items': [{
      'item_name': 'Blue Widget'
    }]
  }
});

1st Party Cookie

Read cookie values:

Variable Type: 1st Party Cookie
Cookie Name: _ga

Use Cases:

• Read GA client ID
• Check session cookies
• Access custom cookies

URL Variable

Parse URL components:

Variable Type: URL
Component Type: Query
Query Key: utm_source

Component Types:

• Full URL: Complete URL
• Protocol: http or https
• Host Name: Domain name
• Port: Port number
• Path: URL path
• Query: Query string or specific parameter
• Fragment: URL hash/anchor

JavaScript Variable

Access global JavaScript variables:

Variable Type: JavaScript Variable
Global Variable Name: document.title

Examples:

• document.title - Page title
• navigator.userAgent - User agent string
• window.innerWidth - Viewport width

Custom JavaScript

Execute JavaScript to return a value:

Variable Type: Custom JavaScript
Custom JavaScript:
function() {
  var path = {{Page Path}};
  return path.split('/')[1] || 'home';
}

Important: Use ES5 syntax only (no const, let, arrow functions)

Pattern Examples:

// Get first path segment
function() {
  var path = {{Page Path}};
  var segments = path.split('/').filter(function(s) { return s; });
  return segments[0] || 'home';
}

// Format currency
function() {
  var value = {{DL - Transaction Total}};
  if (typeof value === 'number') {
    return value.toFixed(2);
  }
  return '0.00';
}

// Check if user is logged in
function() {
  var userId = {{DL - User ID}};
  return userId ? 'logged_in' : 'guest';
}

Constant

Store static values:

Variable Type: Constant
Value: G-XXXXXXXXXX

Use Cases:

• GA4 Measurement IDs
• Pixel IDs
• API keys (non-sensitive)
• Environment-specific values

Lookup Table

Map input values to output values:

Variable Type: Lookup Table
Input Variable: {{Page Path}}
Lookup Table:
  /                   -> home
  /products           -> products
  /about              -> about
  /contact            -> contact
Default Value: other

Regex Table

Map regex patterns to values:

Variable Type: Regex Table
Input Variable: {{Page Path}}
Regex Table:
  ^/$                 -> home
  ^/products/         -> product_detail
  ^/category/         -> category
  ^/blog/             -> blog_post
Default Value: other

Pattern Matching Tips:

• Patterns are matched in order, first match wins
• Use ^ for start anchor, $ for end anchor
• Enable "Ignore Case" if needed
• Enable "Full Matches Only" for stricter matching

Auto-Event Variable

Access data from built-in event listeners:

Variable Type: Auto-Event Variable
Variable Type: Element Attribute
Attribute Name: data-product-id

Variable Types:

• Element: The DOM element
• Element Classes: Class attribute
• Element ID: ID attribute
• Element Target: Target attribute
• Element Text: Text content
• Element URL: href attribute
• Element Attribute: Custom attribute
• History Source: History change source
• History New/Old State: State objects
• History New/Old Fragment: URL fragments

DOM Element

Read content from DOM elements:

Variable Type: DOM Element
Selection Method: CSS Selector
Element Selector: h1.product-title
Attribute Name: (leave blank for text content)

Use Cases:

• Read page title from H1
• Extract product name from element
• Read meta tag content

Element Visibility

Check if element is visible:

Variable Type: Element Visibility
Selection Method: ID
Element ID: product-reviews
Output Type: Boolean

Google Analytics Settings (Legacy)

Store shared GA Universal settings:

Variable Type: Google Analytics Settings
Tracking ID: UA-XXXXXX-X
Fields to Set:
  - anonymizeIp: true
Custom Dimensions:
  - index: 1, dimension value: {{User Type}}

Note: For GA4, use GA4 Configuration tags instead.

Variable Scoping and Persistence

Variable Evaluation

Variables are evaluated:

• When referenced in tags (at tag fire time)
• When used in trigger conditions (at event time)
• When referenced by other variables

Data Layer Persistence

Data layer values persist until:

• Overwritten by a new push
• Page reloads
• Explicitly cleared (using undefined or reset)

// Clear a value
dataLayer.push({
  'previousValue': undefined
});

Advanced Variable Patterns

Chained Variables

Variables can reference other variables:

Variable: Full Event Name
Type: Custom JavaScript
function() {
  return {{Event Category}} + ' - ' + {{Event Action}};
}

Conditional Values

Return different values based on conditions:

function() {
  var pageType = {{DL - Page Type}};
  if (pageType === 'product') {
    return {{DL - Product ID}};
  } else if (pageType === 'category') {
    return {{DL - Category ID}};
  }
  return 'none';
}

Array/Object Handling

Work with complex data structures:

// Get first item from array
function() {
  var items = {{DL - Ecommerce Items}};
  if (items && items.length > 0) {
    return items[0].item_name;
  }
  return '';
}

// Convert array to comma-separated string
function() {
  var items = {{DL - Ecommerce Items}};
  if (!items) return '';
  return items.map(function(item) {
    return item.item_id;
  }).join(',');
}

URL Parameter Extraction

Parse multiple URL parameters:

function() {
  var url = {{Page URL}};
  var params = {};
  var queryString = url.split('?')[1];
  if (queryString) {
    queryString.split('&').forEach(function(pair) {
      var parts = pair.split('=');
      params[parts[0]] = decodeURIComponent(parts[1] || '');
    });
  }
  return params;
}

Variable Naming Conventions

Recommended Format

[Type] - [Description]

Type Prefixes

• DL: Data Layer Variable
• CJS: Custom JavaScript
• URL: URL Variable
• Cookie: Cookie Variable
• Const: Constant
• Lookup: Lookup Table
• Regex: Regex Table
• DOM: DOM Element
• JS: JavaScript Variable

Examples

• DL - User ID
• DL - Product Name
• DL - Transaction Total
• CJS - Page Category
• CJS - Formatted Price
• URL - UTM Source
• URL - UTM Campaign
• Const - GA4 Measurement ID
• Const - FB Pixel ID
• Lookup - Page Type
• Cookie - Session ID

Debugging Variables

Preview Mode

1. Enable Preview mode
2. Click on any event in Summary
3. Open Variables tab
4. View all variable values at that event

Undefined Values

If a variable returns undefined:

• Check data layer has the value
• Verify variable name/path spelling
• Check timing (value pushed after tag fires)
• Verify data layer version setting

Common Issues

Data Layer Variable Not Found:

• Check exact path (case-sensitive)
• Verify value exists in data layer
• Check Data Layer Version setting

Custom JavaScript Errors:

• Check browser console for errors
• Verify ES5 syntax (no const, let, arrow functions)
• Test function logic separately

Lookup/Regex Table Not Matching:

• Check input variable value in Preview
• Verify pattern syntax
• Check pattern order (first match wins)

Resources

• GTM Variable Types
• Built-in Variables Reference
• Data Layer Developer Guide