How do I do custom validation in Polymer Dart - dart

Question

Similar to javascript and the implementation of IronValidatorBehavior how do I do custom validation in Polymer Dart?
I can create a new custom-validator which implements IronValidatorBehavior e.g.
<dom-module id="form-input">
<template>
<style include='shared-styles iron-flex iron-flex-alignment'>
:host {
display: block;
padding: 1em;
}
</style>
<custom-validator id="validator" validator-name="jsonValidator" validator-type="json"></custom-validator>
<paper-textarea label="[[label]]" id="body" name="body" autofocus tabindex="0"
validator="jsonValidator" auto-validate error-message="This is not a valid format"></paper-textarea>
</template>
</dom-module>
The custom-validator is written as
library main_app.custom_validator;
import 'dart:html';
import 'package:polymer/polymer.dart';
import 'package:polymer_elements/iron_validator_behavior.dart' show IronValidatorBehavior;
#PolymerRegister('custom-validator')
class CustomValidator extends PolymerElement with IronValidatorBehavior{
CustomValidator.created() : super.created();
#reflectable
bool validate(e, [_]){
switch(validatorType) {
case 'json':
return textValidator(e);
}
return false;
}
bool textValidator(e){
return false;
}
}

Answer 1

okay, it was a typo, the above works if I change.
<custom-validator id="validator" validator-name="jsonValidator" validator-type="json"></custom-validator>
to
<custom-validator id="validator" validator-name="jsonValidator" validator-check="json"></custom-validator>
The property validatorType needs to be set to its default value of 'validator'. Instead added a new property validatorCheck, where I set the validation method name to be called.
library custom_validator;
import 'dart:mirrors' show reflect;
import 'package:polymer/polymer.dart';
import 'package:polymer_elements/iron_validator_behavior.dart' show IronValidatorBehavior;
import 'package:validator/validator.dart' show isJSON;
#PolymerRegister('custom-validator')
class CustomValidator extends PolymerElement with IronValidatorBehavior{
#property
String validatorCheck;
CustomValidator.created() : super.created();
#reflectable
bool validate(value, [_]){
if(validatorCheck.isNotEmpty) {
Symbol sym = new Symbol(validatorCheck);
return reflect(this).invoke(sym, [value]).reflectee;
}
return false;
}
bool json(String value, [_]){
if(value.isNotEmpty) {
return isJSON(value);
}
return true;
}
}