itemMapProperty — GTM Variable Template for Items

VARIABLES › ITEMS

itemMapProperty EXTENDED Items

Direct (.tpl) Apply (.tpl) Add to GTM

Transforms a single property in every item of an array using a callback function.

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When to Use This

GA4 Ecommerce

Build and transform ecommerce data structures for GA4 event tracking.

Type Conversion

Safely convert between data types — strings, numbers, booleans, arrays, objects.

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Examples

Apply 20% markup to price▶ Try

INPUT

Items (Array of Objects): [{name: "Shirt", price: 100}, {name: "Hat", price: 50}]
Property Name: price
Transform Function: function(x) { return x * 1.2; }

OUTPUT

[{name: "Shirt", price: 120}, {name: "Hat", price: 60}]

Convert names to uppercase▶ Try

INPUT

Items (Array of Objects): [{name: "shirt", color: "blue"}, {name: "hat", color: "red"}]
Property Name: name
Transform Function: function(x) { return x.toUpperCase(); }

OUTPUT

[{name: "SHIRT", color: "blue"}, {name: "HAT", color: "red"}]

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Live Sandbox

This is what you'll see when you open this variable in Google Tag Manager. Hover the icons for details.

itemMapProperty

Read-Only Try Live

Items (Array of Objects)

💾 Array of objects to transform.

Supported formats:
  ✓ Array

Property Name

💾 The property to transform in each object.

Supported formats:
  ✓ String

Transform Function

🎯 A function that receives the current property value and returns the new value (e.g. x => x * 1.2).

Supported formats:
  ✓ Function

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.

Items (Array of Objects) array

💡 Type any text to see the result update live

🎯 Using special value — click input to type instead

Test with:

Falsy undefined null "" empty 0 false NaN

Truthy true 42 "hello" {} empty [] empty {a:1} [1,2,3]

Property Name string

Transform Function function

🔗 Result Handling — Chain Variables

Chain apply-mode variables to the output. Each variable receives the result of the previous one.

itemMapProperty()

+ Chain another variable

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Related Variables

Same category: Items

→ itemAssignDefaults → itemFilterByProperty → itemOmit → itemSet → itemSplitProperty → itemUniqByProperty → pluckProperty → sumProductOfProperties → sumProperty → sumPropertyNested → ⚡ ITEMS › Transformer

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Under the Hood

📜 View Implementation Code

/**
 * Transforms a single property in every object of an array using a callback function.
 * All other properties are preserved unchanged.
 *
 * @param {Array} data.src - Array of objects to transform.
 * @param {string} data.prp - The property name to transform.
 * @param {Function} data.fn - A function that receives the property value and returns the new value.
 * @param {Function|string} [data.out] - Optional output handler.
 *
 * Direct-mode specific parameters:
 * @param {Function} [data.pre] - Optional pre-processor function to transform src before processing.
 *
 * @returns {Array} Array of objects with the specified property transformed.
 *
 * @framework ggLowCodeGTMKit
 */
const getType = require('getType');

const itemMapProperty = function(items, property, transform) {
    if (getType(items) !== 'array') return [];
    if (typeof transform !== 'function') return items;

    return items.map(function(item) {
        if (!item || item[property] === undefined) return item;
        const result = {};
        for (var k in item) {
            if (item.hasOwnProperty(k)) result[k] = item[k];
        }
        result[property] = transform(item[property]);
        return result;
    });
};

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

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

// ===============================================================================
// itemMapProperty(...) - Apply Mode
// ===============================================================================
/*
return function(value, property, transform) {
   property = data.rp1 ? property : data.prp;
   transform = data.rp2 ? transform : data.fn;
   return out(itemMapProperty(value, property, transform));
};
*/

🧪 View Test Scenarios (5 tests)

✅ '[example] Apply 20% markup to price'
✅ '[example] Convert names to uppercase'
✅ Empty array returns empty
✅ Missing property is skipped
✅ Non-function transform returns items unchanged