zod-validation-error

Wrap zod validation errors in user-friendly readable messages.

Features

• User-friendly readable messages, configurable via options;
• Maintain original issues under error.details;
• Extensive tests.

Installation

npm install zod-validation-error

Requirements

• Node.js v.18+
• TypeScript v.4.5+

Quick start

import { z as zod } from 'zod';
import { fromError } from 'zod-validation-error';

// create zod schema
const zodSchema = zod.object({
  id: zod.number().int().positive(),
  email: zod.string().email(),
});

// parse some invalid value
try {
  zodSchema.parse({
    id: 1,
    email: 'foobar', // note: invalid email
  });
} catch (err) {
  const validationError = fromError(err);
  // the error is now readable by the user
  // you may print it to console
  console.log(validationError.toString());
  // or return it as an actual error
  return validationError;
}

Motivation

Zod errors are difficult to consume for the end-user. This library wraps Zod validation errors in user-friendly readable messages that can be exposed to the outer world, while maintaining the original errors in an array for dev use.

Example

Input (from Zod)

[
  {
    "code": "too_small",
    "inclusive": false,
    "message": "Number must be greater than 0",
    "minimum": 0,
    "path": ["id"],
    "type": "number"
  },
  {
    "code": "invalid_string",
    "message": "Invalid email",
    "path": ["email"],
    "validation": "email"
  }
]

Output

Validation error: Number must be greater than 0 at "id"; Invalid email at "email"

API

• ValidationError(message[, options])
• createMessageBuilder(props)
• errorMap
• isValidationError(error)
• isValidationErrorLike(error)
• isZodErrorLike(error)
• fromError(error[, options])
• fromZodIssue(zodIssue[, options])
• fromZodError(zodError[, options])
• toValidationError([options]) => (error) => ValidationError

ValidationError

Main ValidationError class, extending native JavaScript Error.

Arguments

• message - string; error message (required)
• options - ErrorOptions; error options as per JavaScript definition (optional)
  • options.cause - any; can be used to hold the original zod error (optional)

Example 1: construct new ValidationError with message

const { ValidationError } = require('zod-validation-error');

const error = new ValidationError('foobar');
console.log(error instanceof Error); // prints true

Example 2: construct new ValidationError with message and options.cause

import { z as zod } from 'zod';
const { ValidationError } = require('zod-validation-error');

const error = new ValidationError('foobar', {
  cause: new zod.ZodError([
    {
      code: 'invalid_string',
      message: 'Invalid email',
      path: ['email'],
      validation: 'email',
    },
  ]),
});

console.log(error.details); // prints issues from zod error

createMessageBuilder

Creates zod-validation-error's default MessageBuilder, which is used to produce user-friendly error messages.

Meant to be passed as an option to fromError, fromZodIssue, fromZodError or toValidationError.

You may read more on the concept of the MessageBuilder further below.

Arguments

• props - Object; formatting options (optional)
  • maxIssuesInMessage - number; max issues to include in user-friendly message (optional, defaults to 99)
  • issueSeparator - string; used to concatenate issues in user-friendly message (optional, defaults to ";")
  • unionSeparator - string; used to concatenate union-issues in user-friendly message (optional, defaults to ", or")
  • prefix - string or null; prefix to use in user-friendly message (optional, defaults to "Validation error"). Pass null to disable prefix completely.
  • prefixSeparator - string; used to concatenate prefix with rest of the user-friendly message (optional, defaults to ": "). Not used when prefix is null.
  • includePath - boolean; used to provide control on whether to include the erroneous property name suffix or not (optional, defaults to true).

Example

import { createMessageBuilder } from 'zod-validation-error';

const messageBuilder = createMessageBuilder({
  includePath: false,
  maxIssuesInMessage: 3
});

errorMap

A custom error map to use with zod's setErrorMap method and get user-friendly messages automatically.

Example

import { z as zod } from 'zod';
import { errorMap } from 'zod-validation-error';

zod.setErrorMap(errorMap);

isValidationError

A type guard utility function, based on instanceof comparison.

Arguments

• error - error instance (required)

Example

import { z as zod } from 'zod';
import { ValidationError, isValidationError } from 'zod-validation-error';

const err = new ValidationError('foobar');
isValidationError(err); // returns true

const invalidErr = new Error('foobar');
isValidationError(err); // returns false

isValidationErrorLike

A type guard utility function, based on heuristics comparison.

Why do we need heuristics since we can use a simple instanceof comparison? Because of multi-version inconsistencies. For instance, it's possible that a dependency is using an older zod-validation-error version internally. In such case, the instanceof comparison will yield invalid results because module deduplication does not apply at npm/yarn level and the prototype is different.

tl;dr if you are uncertain then it is preferable to use isValidationErrorLike instead of isValidationError.

Arguments

• error - error instance (required)

Example

import { ValidationError, isValidationErrorLike } from 'zod-validation-error';

const err = new ValidationError('foobar');
isValidationErrorLike(err); // returns true

const invalidErr = new Error('foobar');
isValidationErrorLike(err); // returns false

isZodErrorLike

A type guard utility function, based on heuristics comparison.

Why do we need heuristics since we can use a simple instanceof comparison? Because of multi-version inconsistencies. For instance, it's possible that a dependency is using an older zod version internally. In such case, the instanceof comparison will yield invalid results because module deduplication does not apply at npm/yarn level and the prototype is different.

Arguments

• error - error instance (required)

Example

import { z as zod } from 'zod';
import { ValidationError, isZodErrorLike } from 'zod-validation-error';

const zodValidationErr = new ValidationError('foobar');
isZodErrorLike(zodValidationErr); // returns false

const genericErr = new Error('foobar');
isZodErrorLike(genericErr); // returns false

const zodErr = new zod.ZodError([
  {
    code: zod.ZodIssueCode.custom,
    path: [],
    message: 'foobar',
    fatal: true,
  },
]);
isZodErrorLike(zodErr); // returns true

fromError

Converts an error to ValidationError.

What is the difference between fromError and fromZodError? The fromError function is a less strict version of fromZodError. It can accept an unknown error and attempt to convert it to a ValidationError.

Arguments

• error - unknown; an error (required)
• options - Object; formatting options (optional)
  • messageBuilder - MessageBuilder; a function that accepts an array of zod.ZodIssue objects and returns a user-friendly error message in the form of a string (optional).

Notes

Alternatively, you may pass the following options instead of a messageBuilder.

• options - Object; formatting options (optional)
  • maxIssuesInMessage - number; max issues to include in user-friendly message (optional, defaults to 99)
  • issueSeparator - string; used to concatenate issues in user-friendly message (optional, defaults to ";")
  • unionSeparator - string; used to concatenate union-issues in user-friendly message (optional, defaults to ", or")
  • prefix - string or null; prefix to use in user-friendly message (optional, defaults to "Validation error"). Pass null to disable prefix completely.
  • prefixSeparator - string; used to concatenate prefix with rest of the user-friendly message (optional, defaults to ": "). Not used when prefix is null.
  • includePath - boolean; used to provide control on whether to include the erroneous property name suffix or not (optional, defaults to true).

They will be passed as arguments to the createMessageBuilder function. The only reason they exist is to provide backwards-compatibility with older versions of zod-validation-error. They should however be considered deprecated and may be removed in the future.

fromZodIssue

Converts a single zod issue to ValidationError.

Arguments

• zodIssue - zod.ZodIssue; a ZodIssue instance (required)
• options - Object; formatting options (optional)
  • messageBuilder - MessageBuilder; a function that accepts an array of zod.ZodIssue objects and returns a user-friendly error message in the form of a string (optional).

Notes

Alternatively, you may pass the following options instead of a messageBuilder.

• options - Object; formatting options (optional)
  • issueSeparator - string; used to concatenate issues in user-friendly message (optional, defaults to ";")
  • unionSeparator - string; used to concatenate union-issues in user-friendly message (optional, defaults to ", or")
  • prefix - string or null; prefix to use in user-friendly message (optional, defaults to "Validation error"). Pass null to disable prefix completely.
  • prefixSeparator - string; used to concatenate prefix with rest of the user-friendly message (optional, defaults to ": "). Not used when prefix is null.
  • includePath - boolean; used to provide control on whether to include the erroneous property name suffix or not (optional, defaults to true).

They will be passed as arguments to the createMessageBuilder function. The only reason they exist is to provide backwards-compatibility with older versions of zod-validation-error. They should however be considered deprecated and may be removed in the future.

fromZodError

Converts zod error to ValidationError.

Why is the difference between ZodError and ZodIssue? A ZodError is a collection of 1 or more ZodIssue instances. It's what you get when you call zodSchema.parse().

Arguments

• zodError - zod.ZodError; a ZodError instance (required)
• options - Object; formatting options (optional)
  • messageBuilder - MessageBuilder; a function that accepts an array of zod.ZodIssue objects and returns a user-friendly error message in the form of a string (optional).

Notes

Alternatively, you may pass the following options instead of a messageBuilder.

• options - Object; formatting options (optional) user-friendly message (optional, defaults to 99)
  • issueSeparator - string; used to concatenate issues in user-friendly message (optional, defaults to ";")
  • unionSeparator - string; used to concatenate union-issues in user-friendly message (optional, defaults to ", or")
  • prefix - string or null; prefix to use in user-friendly message (optional, defaults to "Validation error"). Pass null to disable prefix completely.
  • prefixSeparator - string; used to concatenate prefix with rest of the user-friendly message (optional, defaults to ": "). Not used when prefix is null.
  • includePath - boolean; used to provide control on whether to include the erroneous property name suffix or not (optional, defaults to true).

They will be passed as arguments to the createMessageBuilder function. The only reason they exist is to provide backwards-compatibility with older versions of zod-validation-error. They should however be considered deprecated and may be removed in the future.

toValidationError

A curried version of fromZodError meant to be used for FP (Functional Programming). Note it first takes the options object if needed and returns a function that converts the zodError to a ValidationError object

toValidationError(options) => (zodError) => ValidationError

Example using fp-ts

import * as Either from 'fp-ts/Either';
import { z as zod } from 'zod';
import { toValidationError, ValidationError } from 'zod-validation-error';

// create zod schema
const zodSchema = zod
  .object({
    id: zod.number().int().positive(),
    email: zod.string().email(),
  })
  .brand<'User'>();

export type User = zod.infer<typeof zodSchema>;

export function parse(
  value: zod.input<typeof zodSchema>
): Either.Either<ValidationError, User> {
  return Either.tryCatch(() => schema.parse(value), toValidationError());
}

MessageBuilder

zod-validation-error can be configured with a custom MessageBuilder function in order to produce case-specific error messages.

Example

For instance, one may want to print invalid_string errors to the console in red color.

import { z as zod } from 'zod';
import { type MessageBuilder, fromError } from 'zod-validation-error';
import chalk from 'chalk';

// create custom MessageBuilder
const myMessageBuilder: MessageBuilder = (issues) => {
  return issues
    // format error message
    .map((issue) => {
      if (issue.code === zod.ZodIssueCode.invalid_string) {
        return chalk.red(issue.message);
      }

      return issue.message;
    })
    // join as string with new-line character
    .join('\n');
}

// create zod schema
const zodSchema = zod.object({
  id: zod.number().int().positive(),
  email: zod.string().email(),
});

// parse some invalid value
try {
  zodSchema.parse({
    id: 1,
    email: 'foobar', // note: invalid email value
  });
} catch (err) {
  const validationError = fromError(err, {
    messageBuilder: myMessageBuilder
  });
  // the error is now displayed with red letters
  console.log(validationError.toString());
}

FAQ

How to distinguish between errors

Use the isValidationErrorLike type guard.

Example

Scenario: Distinguish between ValidationError VS generic Error in order to respond with 400 VS 500 HTTP status code respectively.

import * as Either from 'fp-ts/Either';
import { z as zod } from 'zod';
import { isValidationErrorLike } from 'zod-validation-error';

try {
  func(); // throws Error - or - ValidationError
} catch (err) {
  if (isValidationErrorLike(err)) {
    return 400; // Bad Data (this is a client error)
  }

  return 500; // Server Error
}

How to use ValidationError outside zod

It's possible to implement custom validation logic outside zod and throw a ValidationError.

Example 1: passing custom message

import { ValidationError } from 'zod-validation-error';
import { Buffer } from 'node:buffer';

function parseBuffer(buf: unknown): Buffer {
  if (!Buffer.isBuffer(buf)) {
    throw new ValidationError('Invalid argument; expected buffer');
  }

  return buf;
}

Example 2: passing custom message and original error as cause

import { ValidationError } from 'zod-validation-error';

try {
  // do something that throws an error
} catch (err) {
  throw new ValidationError('Something went deeply wrong', { cause: err });
}

How to use ValidationError with custom "error map"

Zod supports customizing error messages by providing a custom "error map". You may combine this with zod-validation-error to produce user-friendly messages.

Example 1: produce user-friendly error messages using the errorMap property

If all you need is to produce user-friendly error messages you may use the errorMap property.

import { z as zod } from 'zod';
import { errorMap } from 'zod-validation-error';

zod.setErrorMap(errorMap);

Example 2: extra customization using fromZodIssue

If you need to customize some error code, you may use the fromZodIssue function.

import { z as zod } from 'zod';
import { fromZodIssue } from 'zod-validation-error';

const customErrorMap: zod.ZodErrorMap = (issue, ctx) => {
  switch (issue.code) {
    case ZodIssueCode.invalid_type: {
      return {
        message:
          'Custom error message of your preference for invalid_type errors',
      };
    }
    default: {
      const validationError = fromZodIssue({
        ...issue,
        // fallback to the default error message
        // when issue does not have a message
        message: issue.message ?? ctx.defaultError,
      });

      return {
        message: validationError.message,
      };
    }
  }
};

zod.setErrorMap(customErrorMap);

How to use zod-validation-error with react-hook-form?

import { useForm } from 'react-hook-form';
import { zodResolver } from '@hookform/resolvers/zod';
import { errorMap } from 'zod-validation-error';

useForm({
  resolver: zodResolver(schema, { errorMap }),
});

Does zod-validation-error support CommonJS

Yes, zod-validation-error supports CommonJS out-of-the-box. All you need to do is import it using require.

Example

const { ValidationError } = require('zod-validation-error');

Contribute

Source code contributions are most welcome. Please open a PR, ensure the linter is satisfied and all tests pass.

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License

MIT