zod-validation-error

Wrap zod validation errors in user-friendly readable messages.

Features

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

Installation

npm install zod-validation-error

Requirements

• Node.js v.16+

Quick start

import { z as zod } from 'zod';
import { fromZodError } 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 = fromZodError(err);
  // the error now is readable by the user
  // you may print it to console
  // or return it via an API
  console.log(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[, details])
• errorMap
• isValidationError(error)
• isValidationErrorLike(error)
• fromZodIssue(zodIssue[, options])
• fromZodError(zodError[, options])
• toValidationError([options]) => (error) => ValidationError

ValidationError

Main ValidationError class, extending native JavaScript Error.

Arguments

• message - string; error message (required)
• details - Array<zod.ZodIssue>; error details (optional)

Example

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

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

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

const err = new ValidationError('foobar', { details: [] });
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 if we have 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.

In most cases, it is safer to use isValidationErrorLike than isValidationError.

Arguments

• error - error instance (required)

Example

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

const err = new ValidationError('foobar', { details: [] });
isValidationErrorLike(err); // returns true

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

fromZodIssue

Converts a single zod issue to ValidationError.

Arguments

• zodIssue - zod.ZodIssue; a ZodIssue instance (required)
• 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.

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)
  • 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.

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 } 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<Error, User> {
  return Either.tryCatch(() => schema.parse(value), toValidationError());
}

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

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;
}

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);

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.

We are hiring

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License

MIT