dateToUnixTimestamp — GTM Variable Template for Date

VARIABLES › DATE

dateToUnixTimestamp EXTENDED Date

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

Converts a date string to Unix timestamp in milliseconds.

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When to Use This

Date Formatting

Format and transform date values into human-readable or machine-readable strings.

Type Conversion

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

Date & Time

Calculate durations, differences, and time-based operations on date values.

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Examples

Date to Unix timestamp▶ Try

INPUT

Date String: 2024-01-15

OUTPUT

1705276800000

Epoch returns 0▶ Try

INPUT

Date String: 1970-01-01

OUTPUT

0

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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.

dateToUnixTimestamp

Read-Only Try Live

Date String

💾 Date string in YYYY-MM-DD 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.

Date String string

💡 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.

dateToUnixTimestamp()

+ Chain another variable

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Related Variables

Same category: Date

→ addDays → basicDateToExtended → calculateDaysDifference → calculateLeadTime → currentTimestamp → daysToMilliseconds → extendedDateToBasic → getDayIndexFromDateString → getDayName → getDayNameFromDateString → getDayNameShort → getHourOfDay → getMonthName → getMonthNameShort → hoursToMilliseconds → isBusinessHours → isWeekend → millisecondsToDays → millisecondsToHours → millisecondsToMinutes → millisecondsToSeconds → minutesToMilliseconds → reverseDateCompactDay1st → reverseDateCompactYear1st → reverseDateSlash → secondsToMilliseconds → subtractDays → timestampToDayIndex → unixTimestampToDate

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Under the Hood

📜 View Implementation Code

/**
* Convert a date in YYYY-MM-DD format to Unix timestamp (milliseconds since epoch) without using the Date object.
*
* @param {string} data.src - Date string in YYYY-MM-DD format.
* @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 conversion.
*
* @returns {number|undefined} Unix timestamp in milliseconds, or undefined if input is invalid.
*
* @framework ggLowCodeGTMKit
*/
const makeNumber = require('makeNumber');
const Math = require('Math');

const dateToUnixTimestamp = function(dateStr) {
   if (typeof dateStr !== 'string') { return undefined; }
   const reDateFormatISO8601 = "^(\\d{4})-(\\d{2})-(\\d{2})$";
   const dateMatchParts = dateStr.match(reDateFormatISO8601);
   if (dateMatchParts === null) { return undefined; }

   const year = makeNumber(dateMatchParts[1]);
   const month = makeNumber(dateMatchParts[2]);
   const day = makeNumber(dateMatchParts[3]);

   function calculateDaysSinceEpoch(year, month, day) {
       function isLeapYear(year) {
           return (year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0);
       }

       const daysInFebruary = isLeapYear(year) ? 29 : 28;

       // Days in each month including a dummy value for index 0
       const daysInMonth = [0, 31, daysInFebruary, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];

       if (day > daysInMonth[month]) {
           return undefined;
       }

       // Days from 1970 to the year before
       let totalDays = 0;
       for (let y = 1970; y < year; y++) {
           totalDays += isLeapYear(y) ? 366 : 365;
       }

       // Add days from months in the current year
       for (let m = 1; m < month; m++) {
           totalDays += daysInMonth[m];
       }

       // Add days from the current month
       totalDays += day - 1;

       return totalDays;
   }

   const daysSinceEpoch = calculateDaysSinceEpoch(year, month, day);
   return daysSinceEpoch !== undefined ? daysSinceEpoch * 24 * 60 * 60 * 1000 : undefined;
};

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

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

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

🧪 View Test Scenarios (5 tests)

✅ '[example] Date to Unix timestamp'
✅ '[example] Epoch returns 0'
✅ Leap year date - should calculate correctly
✅ Invalid date format - should return undefined
✅ Invalid day in month - should return undefined