simple validation functions in typescript

validations.ts

const emailRegexp =
  /[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?/i;
const alphabeticRegexp = /^[a-zA-Z\s]*$/g;
const specialsRegexp = /[`\+=\?!\]\[\$}{:\/&\\@#\|<>;]/g;
const nonNumericRegexp = /\D/g;

export const isEmail = (email?: string | number | undefined) => {
  return Boolean(`${email ?? ''}`.match(emailRegexp));
};

export const isAlphabetic = (value?: string | number | undefined) => {
  return Boolean(`${value ?? ''}`.length > 0 && alphabeticRegexp.test(`${value ?? ''}`));
};

export const hasSpecialCharacters = (value?: string | number | undefined) => {
  return Boolean(`${value ?? ''}`.length > 0 && specialsRegexp.test(`${value ?? ''}`));
};

export const isNumeric = (value?: string | number | undefined) => {
  return Boolean(`${value ?? ''}`.length > 0 && !nonNumericRegexp.test(`${value ?? ''}`));
};

export const isDefined = (value?: string | number | undefined) => {
  return Boolean(typeof value !== 'undefined');
};

export const isNonEmpty = (value?: string | number | undefined) => {
  return `${value ?? ''}`.length > 0;
};

export const isNonEmptyString = (value?: string | number | undefined) => {
  return `${value ?? ''}`.trim().length > 0;
};

export const isGreaterThanLength = (length: number) => (value?: string | number | undefined) => {
  return `${value ?? ''}`.length > length;
};

export const isLessThanLength = (length: number) => (value?: string | number | undefined) => {
  return `${value ?? ''}`.length < length;
};

export const isEqualsToLength = (length: number) => (value?: string | number | undefined) => {
  return `${value ?? ''}`.length === length;
};

export const isEqual = (expected: string | number | undefined) => (value?: string | number | undefined) => {
  return `${value ?? ''}` === expected;
};

export const isGreaterThan = (expected: string | number | undefined) => (value?: string | number | undefined) => {
  return parseInt(`${value ?? '0'}`) > parseInt(`${expected ?? '0'}`);
};

export const isSmallerThan = (expected: string | number | undefined) => (value?: string | number | undefined) => {
  return parseInt(`${value ?? '0'}`) < parseInt(`${expected ?? '0'}`);
};

export const OR =
  (...fns: ((value: string | number | undefined) => boolean)[]) =>
  (value?: string | number | undefined) => {
    return fns.some((fn) => fn(value));
  };

export const AND =
  (...fns: ((value: string | number | undefined) => boolean)[]) =>
  (value?: string | number | undefined) => {
    return fns.every((fn) => fn(value));
  };

export const isNot =
  (validator: (value?: string | number | undefined) => boolean) => (value?: string | number | undefined) => {
    return !validator(value);
  };

export const validators = {
  isEmail,
  isNumeric,
  isNonEmpty,
  isGreaterThanLength,
  isLessThanLength,
  isEqualsToLength,
  isNonEmptyString,
  isNot,
  isEqual,
  isDefined,
  OR,
};

/**
 *
 * @param value value to be validated
 * @param validationFns single or multiple functions of validation, function or keyof predefined validators
 * @returns boolean
 */
export const validate = (
  value: string | number | undefined,
  ...validationFns: ((value: string | number | undefined) => boolean)[]
) => {
  return validationFns.every((fn) => fn(value));
};

Example usage;

const something = validate(
  myVariable,
  isDefined,
  isNonEmptyString,
  isEqualsToLength(4),
  isNumeric
);

const somethingElse = validate(
    myOtherVariable,
    OR(
        OR(
          isNot(isDefined),
          isNot(isNonEmptyString)
        ),
      	AND(
          isDefined,
          isNumeric
        )
    ),
);