reduceRight — GTM Variable Template for Array

VARIABLES › ARRAY

reduceRight EXTENDED Array

Direct (.tpl) Apply (.tpl)

Reduces an array from right to left using a callback function and an optional initial value.

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Examples

Reverse concatenation▶ Try

INPUT

Array To Reduce: ['a', 'b', 'c', 'd']
Reducer Function: function(acc, val) { return acc + val; }
Initial Value:
Use Initial Value: true

OUTPUT

dcba

Sum from right▶ Try

INPUT

Array To Reduce: [1, 2, 3, 4, 5]
Reducer Function: function(acc, val) { return acc + val; }
Initial Value: undefined
Use Initial Value: false

OUTPUT

15

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GTM Configuration

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reduceRight

Read-Only Try Live

Array To Reduce

💾 The array to reduce from right to left.

Supported formats:
  ✓ Array

Reducer Function

💾 A reducer function of the form (accumulator, currentValue) => nextAccumulator.

Supported formats:
  ✓ Function

Initial Value

💾 An optional initial value for the accumulator.

Supported formats:
  ✓ Any

Use Initial Value

💾 Whether to use the initial value.

Options:
  ✓ Yes/No

YesNo

Input Setup

Input Function (optional)

⚙️ Optional pre-processing function applied to the array before internal logic (e.g., filter elements, sort array). Internal transformations will still apply afterward.

Result Handling

Output Function (optional)

⚙️ Optional function to apply to the result before returning it (e.g., val => Math.round(val), val => val.toString() for string conversion). Useful for chaining transformations on the output.

Array To Reduce 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]

Reducer Function function

Initial Value any

🔗 Result Handling — Chain Variables

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

reduceRight()

+ Chain another variable

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Related Variables

Same category: Array

→ chunk → compact → dropItems → dropItemsRight → every → filterArray → find → findIndexByCallback → findIndexByRegex → flatten → head → includesAll → includesAny → includesNone → indexOf → join → last → lastIndexOf → reduce → reverse → selectFromArray → some → sort → tail → takeItems → takeItemsRight → uniq → wrapInArray

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Under the Hood

📜 View Implementation Code

/**
 * Reduces an array from right to left using a callback function and an optional initial value.
 *
 * @param {Array} data.arr - The array to reduce.
 * @param {Function} data.fnc - A reducer function of the form (accumulator, currentValue) => nextAccumulator.
 * @param {*} data.ini - An optional initial value for the accumulator.
 * @param {boolean} data.use - Whether to use the initial value.
 * @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 arr before reducing.
 * 
 * @returns {*|undefined} The final accumulated result from the right-to-left reduce operation. Returns undefined if the input is not a valid array or the callback is not a function.
 *
 * @framework ggLowCodeGTMKit
 */
const getType = require('getType');
const reduceRight = function(array, callback, initialValue, useInitial) {
    if (getType(array) !== 'array' || typeof callback !== 'function') {
        return undefined;
    }
    return useInitial ? array.reduceRight(callback, initialValue) : array.reduceRight(callback);
};
const safeFunction = fn => typeof fn === 'function' ? fn : x => x;
const out = safeFunction(data.out);
// ===============================================================================
// reduceRight - Direct mode
// ===============================================================================
const applyCast = (castFn, value) => safeFunction(castFn)(value);
const processedArray = applyCast(data.pre, data.arr);
return out(reduceRight(processedArray, data.fnc, data.ini, data.use));
// ===============================================================================
// reduceRight(...) – Apply Mode
// ===============================================================================
/*
return function(array, callback, initialValue, useInitial) {
   callback = data.rp1 ? data.fnc : callback;
   return out(reduceRight(array, callback, data.ini, data.use));
};
*/

🧪 View Test Scenarios (11 tests)

✅ '[example] Reverse concatenation'
✅ Subtract numbers from right to left with initial value
✅ Build array from right to left with initial value
✅ Flatten nested arrays from right to left with initial value
✅ '[example] Sum from right'
✅ Single element array with initial value - should return combined result
✅ Single element array without initial value - should return the element
✅ Empty array with initial value - should return initial value
✅ Non-function callback - should return undefined
✅ Compose functions from right to left
✅ Build nested structure from right to left with initial value