isJSON — GTM Variable Template for Condition

VARIABLES › CONDITION

isJSON EXTENDED Condition

Direct (.tpl) Apply (.tpl)

Checks if a given input is valid JSON.

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Examples

Valid JSON returns true▶ Try

INPUT

Value To Check: {"key": "value"}

OUTPUT

true

Invalid JSON returns false▶ Try

INPUT

Value To Check: {key: "value"}

OUTPUT

false

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GTM Configuration

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isJSON

Read-Only Try Live

Value To Check

💾 The value to check.

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.

Value To Check object

💡 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.

isJSON()

+ Chain another variable

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Related Variables

Same category: Condition

→ isArray → isDefined → isEmpty → isEmptyString → isEqualTo → isFalsy → isFunction → isGreaterThan → isGreaterThanOrEqualTo → isInRange → isInfinity → isInteger → isLessThan → isLessThanOrEqualTo → isNaN → isNotArray → isNotEmptyString → isNotFunction → isNotJSON → isNotNaN → isNotNull → isNotNumber → isNotObject → isNotString → isNotURL → isNull → isNumber → isObject → isPrimitive → isSHA256 → isString → isStringifiedNumber → isTruthy → isURL → isUndefined → isUnixTimestamp → isUnixTimestampMilliseconds → isUnixTimestampSeconds → isValidNumber

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Under the Hood

📜 View Implementation Code

/**
 * Checks if a given string is valid JSON by parsing it and ensuring the result is not undefined.
 * 
 * @param {any} data.src - The value to check.
 * @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} True if the value is valid JSON, false otherwise.
 *
 * @framework ggLowCodeGTMKit
 */
const JSON = require('JSON');
const isJSON = function(value) {
	return JSON.parse(value) !== undefined;
};
const safeFunction = fn => typeof fn === 'function' ? fn : x => x;
const out = safeFunction(data.out);
// ===============================================================================
// isJSON - Direct mode
// ===============================================================================
const applyCast = (castFn, value) => safeFunction(castFn)(value);
const value = applyCast(data.pre, data.src);
return out(isJSON(value));
// ===============================================================================
// isJSON() – Apply Mode
// ===============================================================================
/*
return function(value) {
   return out(isJSON(value));
};
*/

🧪 View Test Scenarios (4 tests)

✅ '[example] Valid JSON returns true'
✅ '[example] Invalid JSON returns false'
✅ Object value - should return false
✅ Number value - should return true