reverseDateCompactDay1st — GTM Variable Template for Date

VARIABLES › DATE

reverseDateCompactDay1st EXTENDED Date

Direct (.tpl) Apply (.tpl)

Reverses a compact date string from "ddmmyyyy" to "yyyymmdd" format.

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Examples

Reverse ddmmyyyy to yyyymmdd▶ Try

INPUT

Compact Date String: 25122024

OUTPUT

20241225

Invalid length returns undefined▶ Try

INPUT

Compact Date String: 2512202

OUTPUT

undefined

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GTM Configuration

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reverseDateCompactDay1st

Read-Only Try Live

Compact Date String

💾 The compact date string with no separators, starting with day (ddmmyyyy format).

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.

Compact Date String number

💡 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]

🔗 Result Handling — Chain Variables

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

reverseDateCompactDay1st()

+ Chain another variable

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Related Variables

Same category: Date

→ calculateDaysDifference → currentTimestamp → getDayIndexFromDateString → getDayName → getDayNameFromDateString → getDayNameShort → getMonthName → getMonthNameShort → reverseDateCompactYear1st → reverseDateSlash → timestampToDayIndex

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Under the Hood

📜 View Implementation Code

/**
* Reverse a compact date string from "ddmmyyyy" to "yyyymmdd".
* 
* @param {string} data.src - The compact date string with no separators, starting with day.
* @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 reversing.
* 
* @returns {string|undefined} The reversed date string, or undefined if the input is invalid.
*
* @framework ggLowCodeGTMKit
*/
const reverseDateCompactDay1st = function(date) {
   if (typeof date !== 'string' || date.length !== 8) { return undefined; }
   const day = date.substring(0, 2);
   const month = date.substring(2, 4);
   const year = date.substring(4, 8);
   return year + month + day;
};

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

// ===============================================================================
// reverseDateCompactDay1st - Direct mode
// ===============================================================================
const applyCast = (castFn, value) => safeFunction(castFn)(value);
const value = applyCast(data.pre, data.src);
return out(reverseDateCompactDay1st(value));

// ===============================================================================
// reverseDateCompactDay1st() – Apply Mode
// ===============================================================================
/*
return function(value) {
  return out(reverseDateCompactDay1st(value));
};
*/

🧪 View Test Scenarios (5 tests)

✅ '[example] Reverse ddmmyyyy to yyyymmdd'
✅ Valid date with leading zeros - reverses correctly
✅ Valid date end of year - reverses correctly
✅ '[example] Invalid length returns undefined'
✅ Non-string input - returns undefined