Validations helpers

When writing custom rules, some checks or validations can become tedious, especially when handling values that might be null, undefined, or unset. It's also a best practice to verify whether a field is "filled" before proceeding with validation.

To simplify this process, Regle provides a set of utility functions to assist in creating custom rules.

These utilities can be accessed via:

import { isFilled, isEmpty, getSize, ... } from '@regle/rules';

Runtime and Type guards

isFilled

This is almost a must have for optional fields. It checks if any value you provided is defined (including arrays and objects). You can base your validator result on this.

isFilled also acts as a type guard.

import { createRule } from '@regle/core';
import { isFilled } from '@regle/rules';

const rule = createRule({
  validator(value: unknown) {
    if (isFilled(value)) {
      return check(value);
    }
    return true;
  },
  message: 'Error'
})

isEmpty

This is the inverse of isFilled. It will check if the value is in any way empty (including arrays and objects)

isEmpty also acts as a type guard.

import { createRule, type Maybe } from '@regle/core';
import { isEmpty } from '@regle/rules';

const rule = createRule({
  validator(value: Maybe<string>) {
    if (isEmpty(value)) {
      return true;
    }
    return check(value);
  },
  message: 'Error'
})

isNumber

This is a type guard that will check if the passed value is a real Number. This also returns false for NaN, so this is better than typeof value === "number".

import { createRule, type Maybe } from '@regle/core';
import { isFilled, isNumber } from '@regle/rules';

const rule = createRule({
  validator(value: Maybe<number | string>) {
    if (isFilled(value) && isNumber(value)) {
      return checkNumber(value);
    }
    return true;
  },
  message: 'Error'
})

isDate

This is a useful helper that can check if the provided value is a Date, it is used internally for date rules. This can also check strings.

import { createRule, type Maybe } from '@regle/core';
import { isFilled, isDate } from '@regle/rules';

const rule = createRule({
  validator(value: Maybe<string | Date>) {
    if (isFilled(value) && isDate(value)) {
      return checkDate(value);
    }
    return true;
  },
  message: 'Error'
})

Operations utils

getSize

This helper will return the length of any data type you pass. It works with strings, arrays, objects and numbers.

import { createRule, type Maybe } from '@regle/core';
import { isFilled, getSize } from '@regle/rules';

const rule = createRule({
  validator(value: Maybe<string | Array<number>>) {
    if (isFilled(value)) {
      return getSize(value) > 6;
    }
    return true;
  },
  message: 'Error'
})

matchRegex

This utility can take multiple regular expressions as arguments. It checks the input's validity and tests it against the provided regex patterns.

import { createRule, type Maybe } from '@regle/core';
import { isFilled, matchRegex } from '@regle/rules';

const rule = createRule({
  validator(value: Maybe<string>, ...regexps: RegExp[]) {
    if (isFilled(value)) {
      return matchRegex(value, ...regexps);
    }
    return true;
  },
  message: 'Error'
})

Coerce utils

toNumber

This utility converts any string (or number) into a number using the Number constructor.

WARNING

This helper returns NaN if the input cannot be coerced, which is technically still a number.

It can be safe to also check for isNaN additionally.

toDate

This utility will coerce any string, number or Date value into a Date using the Date constructor.