startsWith — GTM Variable Template for String

VARIABLES › STRING

startsWith EXTENDED String

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

Checks if the given string starts with the specified substring. Returns true if match found, false otherwise.

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When to Use This

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Examples

String starts with match▶ Try

INPUT

String To Check: hello world
Search Term: hello

OUTPUT

true

No match at start▶ Try

INPUT

String To Check: hello world
Search Term: world

OUTPUT

false

Null input returns false▶ Try

INPUT

String To Check: null
Search Term: test

OUTPUT

false

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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.

startsWith

Read-Only Try Live

String To Check

💾 The string or value to check.

Supported formats:
  ✓ String
  ✓ Number
  ✓ Object

Search Term

💾 The substring to check if it is at the start of the string.

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.

String To Check 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]

Search Term string

🔗 Result Handling — Chain Variables

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

startsWith()

+ Chain another variable

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Related Variables

Same category: String

→ charAt → collapseWhitespace → concat → countWordsInString → endsWith → extract → extractFirstSegment → extractNumber → fromBase64 → indexOf → left → matchAll → matchRegex → normalizeEmail → normalizePhone → padEnd → padStart → parseJSON → replaceAll → replaceAllWithRegex → replaceFirst → right → safeSplit → search → slice → slugify → split → stripAccents → stripHtml → substringAfter → substringBefore → test → toBase64 → toCamelCase → toJsonString → toKebabCase → toLocaleLowerCase → toLocaleUpperCase → toLowerCase → toNumber → toSnakeCase → toStartCase → toString → toStringRepresentation → toUpperCase → toUpperFirst → trim → trimEnd → trimStart → truncate

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Under the Hood

📜 View Implementation Code

/**
 * Checks if the given string starts with the specified substring.
 *
 * @param {any} data.src - The string or value to check.
 * @param {string} data.str - The substring to check if it is at the start of src.
 * @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 checking.
 *
 * @returns {boolean} Returns true if the src starts with the str, otherwise returns false.
 *
 * @framework ggLowCodeGTMKit
 */
const startsWith = function(searchData, searchTerm) {
    if (searchData == null || typeof searchTerm !== 'string') {
        return false;
    }
    const searchDataString = searchData.toString();
    return searchDataString.substring(0, searchTerm.length) === searchTerm;
};
const safeFunction = fn => typeof fn === 'function' ? fn : x => x;
const out = safeFunction(data.out);
// ===============================================================================
// startsWith - Direct mode
// ===============================================================================
const applyCast = (castFn, value) => safeFunction(castFn)(value);
const value = applyCast(data.pre, data.src);
return out(startsWith(value, data.str));
// ===============================================================================
// startsWith(...) – Apply Mode
// ===============================================================================
/*
return function(value, searchTerm) {
   searchTerm = data.rp1 ? searchTerm : data.str;
   return out(startsWith(value, searchTerm));
};
*/

🧪 View Test Scenarios (5 tests)

✅ '[example] String starts with match'
✅ '[example] No match at start'
✅ Empty string with empty term - should return true
✅ Number starting with specified digits - should return true
✅ '[example] Null input returns false'