property-validators.ts

import { component, property, JoistElement } from '@joist/component';

function isString(val: unknown) {
  if (typeof val === 'string') {
    return null;
  }

  return { message: 'error' };
}

function isLongerThan(length: number) {
  return function (val: string) {
    if (val.length > length) {
      return null;
    }

    return { message: 'Incorrect length' };
  }


@component()
class MyElement extends JoistElement {
  @property(isString, isLongerThan(2))
  public hello = 'Hello World';
}