some validators to use with formstate

validators.tsx

import { Validator, applyValidators } from 'formstate';

/** One of the easy to validate values */
export type SimpleValue = string | boolean | number | null | undefined;

/**
 * - Whitespace strings / false / null / undefined  are considered invalid
 */
export const required: Validator<SimpleValue> = (value) => {
  const error = "Value Required";
  if (value == null) {
    return error;
  }
  if (typeof value === 'string' && !value.trim()) {
    return error;
  }
  else if (value === false) {
    return error;
  }
  return null;
}

export const email: Validator<string> = (value: string) => {
  if (value == null || value == '') return null;
  if (typeof value !== 'string') {
    return "Email must be a string";
  }
  value = value.trim();
  // Src : http://emailregex.com/
  if (!/^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/g.exec(value)) {
    return "Not a valid email address";
  }
  return null;
}

export const minLength = (minValue: number): Validator<string> => {
  return (value: string) => {
    if (value == null || value == '') return null;
    if (value.length < minValue) {
      return 'Minimum length required is ' + minValue.toString();
    }
    return null;
  }
}

export const maxLength = (maxValue: number): Validator<string> => {
  return (value: string) => {
    if (value == null || value == '') return null;
    if (value.length > maxValue) {
      return 'Maximum length allowed is ' + maxValue.toString();
    }
    return null;
  }
}

export const exactLength = (length: number): Validator<string> => {
  return (value: string) => {
    if (value == null || value == '') return null;
    if (value.length !== length) {
      return 'Length must be ' + length.toString();
    }
    return null;
  }
}

/**
 * Allows you to customize the message for validators
 */
export function withMessage<T>(message: string, ...validators: Validator<T>[]): Validator<T> {
  return (value: T) => applyValidators(value, validators).then(res => {
    return res ? message : res
  });
}