Custom Validators

createValidator()

Creates a custom validator function that can be passed into a schema.

createValidator(cb: (fieldKey: string, value: unknown) => ErrorReturnTypes, customMessage?: string)

Params

Name	Type	Description
cb	(fieldKey: string, value: unknown) => ErrorReturnTypes	A callback that gets called to validate a value. The fieldKey is the name of the field in the schema, the value is the value to validate. You can return any of the error types (null, string or string[])
customMessage	string, undefined	This is the custom message to use if there is a error. It will override kind of error you return in the callback.

Examples

Basic Custom Validator

This is the most basic way to create a custom validator however it has one main limitation of not using a user provided overriding error message. This will return a error if the value is true.

import { createValidator } from "super-validator";
export const customValidator = () => createValidator((fieldKey, value) => {    // Validation Logic    if (value === true) {        return `This is a error for: '${fieldKey}'`; // If there is a error return a string. You can also use the fieldName in the error message.    }    return null; // If validation passes return null.});

Custom Validator With User Provided Message

This allows a user to pass in a message when creating a schema. NOTE: This will override any error message(s) returned from the validator.

import { createValidator } from "super-validator";
export const customValidator = (customMessage) => createValidator((fieldKey, value) => {    // Validation Logic    if (value === true) {        return `This is a error for: '${fieldKey}'`;    }    return null; // If validation passes return null.}, customMessage);

Custom Validator Multiple Errors

To use return multiple errors you just need to return a array instead of a string for the error(s). It's important to note that in this example if a user passes a customMessage it will override any array you return and only return the provided string.

import { createValidator } from "super-validator";
export const customValidator = (customMessage) => createValidator((fieldKey, value) => {    const errors = [];    if (value === true) {        errors.push("This is a error!"); // Add this error to array.    }
    if (value === true) {        errors.push("This is a 2nd error!"); // Add this 2nd error to array.    }    return errors; // Return the array if it is empty there are no errors.  }, customMessage);

Custom Validator With Parameters

You can also take in custom parameters when making a validator. In the below example you will pass in a number (n) that is used to check if the value is greater than n.

import { createValidator } from "super-validator";
export const customValidator = (greaterThan, customMessage) => createValidator((fieldKey, value) => {    if (value <= greaterThan) {        return `'${fieldKey}' has to be greater than ${greaterThan}.`;    }    return null;}, customMessage);

Typescript

Here is a example of a validator in Typescript that will return a error if the value is less than the provided value.

import { createValidator, ErrorReturnTypes, ValidatorFunction } from "super-validator";
export const min = (minValue: number, customMessage?: string): ValidatorFunction<number> =>    createValidator<number>((fieldKey: string, value: number): ErrorReturnTypes => {        if (value < minValue) {            return `${value} is less than ${minValue}`        }        return null    }, customMessage)