customJS static method

String? customJS(String? value, String jsCode, Map<String, dynamic> formData, { String? fieldName, })

Custom JavaScript validation.

Executes JavaScript code to validate the input value. The JavaScript code has access to:

• input: the current field value
• data: entire form data
• valid: boolean or string (error message)

Example:

FormioValidators.customJS(
  'magic',
  "valid = (input === 'magic') ? true : 'Must be magic';",
  {},
)

Form.io format:

{
  "validate": {
    "custom": "valid = (input.length > 5) ? true : 'Too short';"
  }
}

Implementation

static String? customJS(
  String? value,
  String jsCode,
  Map<String, dynamic> formData, {
  String? fieldName,
}) {
  try {
    // Import JavaScript evaluator
    // ignore: implementation_imports
    final jsEvaluator = _getJavaScriptEvaluator();

    if (jsEvaluator == null) {
      return 'JavaScript validation not available';
    }

    // Create JavaScript context
    final context = {
      'input': value,
      'data': formData,
      'valid': true,
    };

    // Validate code safety
    jsEvaluator.validateCode(jsCode);

    // Execute JavaScript
    final result = jsEvaluator.evaluate(jsCode, context);

    // Form.io validation result format:
    // - true or 'true' means valid
    // - string means error message
    // - false or anything else means generic error
    if (result == true || result == 'true' || result == 'True') {
      return null; // Valid
    } else if (result is String && result.isNotEmpty) {
      return result; // Custom error message
    } else {
      return '${fieldName ?? "This field"} is invalid.';
    }
  } catch (e) {
    debugPrint('Custom validation error for ${fieldName ?? "field"}: $e');
    return 'Validation failed: ${e.toString()}';
  }
}