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ggLowCodeGTMKit

itemSet — GTM Variable Template for Items

VARIABLES › ITEMS
itemSet CORE Items
Direct (.tpl) Apply (.tpl)

Adds or overwrites a property on each object in an array using a callback or static value.

When to Use This

GA4 Ecommerce

Build and transform ecommerce data structures for GA4 event tracking.

Examples

Add computed property
INPUT
Source Array: [
{price: 10, quantity: 2},
{price: 20, quantity: 3}
]
Value Function: function(item) { return item.price * item.quantity; }
Property Key: total
Value Mode: fn
OUTPUT
[ {price: 10, quantity: 2, total: 20}, {price: 20, quantity: 3, total: 60} ]
Set static value
INPUT
Source Array: [
{price: 10, quantity: 2},
{price: 20, quantity: 3}
]
Property Key: currency
Value Mode: val
Static Value: EUR
OUTPUT
[ {price: 10, quantity: 2, currency: 'EUR'}, {price: 20, quantity: 3, currency: 'EUR'} ]

GTM Configuration

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

itemSet
Source Array
💾 The array of objects to process.

Supported formats:
  ✓ Items variable: {{ecommerce.items}}
  ✓ Array literal: [{price: 10, quantity: 2}]
Property Key
💾 The property name to add or overwrite on each item.

Supported formats:
  ✓ New property: "total", "margin", "currency"
  ✓ Existing property: "price" (will be overwritten)
Value Mode
💾 How to determine the value to set on each item.

  ✓ Computed: uses a callback function receiving the item
  ✓ Static: sets the same value on every item
Value Function
💾 A function that receives each item and returns the value to set.

Supported formats:
  ✓ applyFromObject: {{applyFromObject(...)}}
  ✓ Custom function: item => Math.round(item.price)
Static Value
💾 The static value to set on every item.

Supported formats:
  ✓ String: "EUR", "active"
  ✓ Number: 1, 0
  ✓ Variable: {{currency}}
Input Setup
Input Function (optional)
⚙️ Optional pre-processing function applied to the source array before processing.
Result Handling
Output Function (optional)
⚙️ Optional function to apply to the resulting array before returning it (e.g., arr => arr.filter(x => x.total > 0) to keep only items with a positive total).
Source Array array
💡 Type any text to see the result update live
🎯 Using special value — click input to type instead
Test with:
Falsy
Truthy
Property Key string
Value Function function
Static Value number
🔗 Result Handling — Chain Variables
Chain apply-mode variables to the output. Each variable receives the result of the previous one.
itemSetProperty()

Related Variables

Same category: Items

→ itemAssignDefaults → itemMapProperties → itemOmit → itemPluckProperty → map → sumProductOfProperties → sumProperty → sumPropertyByPath

Under the Hood

📜 View Implementation Code
/**
 * Adds or overwrites a property on each object in an array using a static value or a callback function.
 * Preserves all existing properties of each item.
 *
 * @param {Array} data.src - The array of objects to process.
 * @param {string} data.key - The property name to set on each item.
 * @param {string} data.mod - Value mode: "fn" for computed value, "val" for static value.
 * @param {Function} [data.fn] - A function that receives the item and returns the value to set (when mod="fn").
 * @param {*} [data.val] - Static value to set on each item (when mod="val").
 * @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} A new array of objects with the specified property added or overwritten.
 *
 * @framework ggLowCodeGTMKit
 */
const getType = require('getType');
const itemSetProperty = function(arr, key, fn, val) {
    if (getType(arr) !== 'array') return [];
    if (!key) return arr;

    const getValue = typeof fn === 'function'
        ? fn
        : function() { return val; };

    return arr.map(function(item) {
        if (item == null || typeof item !== 'object') return item;
        const result = {};
        for (const k in item) {
            if (item.hasOwnProperty(k)) result[k] = item[k];
        }
        result[key] = getValue(item);
        return result;
    });
};
const safeFunction = fn => typeof fn === 'function' ? fn : x => x;
const out = safeFunction(data.out);
// ===============================================================================
// itemSetProperty - Direct mode
// ===============================================================================
const applyCast = (castFn, value) => safeFunction(castFn)(value);
const value = applyCast(data.pre, data.src);
const fn = data.mod === 'fn' ? data.fn : undefined;
const val = data.mod === 'val' ? data.val : undefined;
return out(itemSetProperty(value, data.key, fn, val));
// ===============================================================================
// itemSetProperty(...) – Apply Mode
// ===============================================================================
/*
return function(arr) {
    const fn = data.mod === 'fn' ? data.fn : undefined;
    const val = data.mod === 'val' ? data.val : undefined;
    return out(itemSetProperty(arr, data.key, fn, val));
};
*/
🧪 View Test Scenarios (6 tests)
✅ '[example] Add computed property'
✅ '[example] Set static value'
✅ Overwrite existing property with static value
✅ Preserves all existing properties
✅ Invalid src returns empty array
✅ Invalid fn falls back to static undefined